Update packer.go to cleanup plugin clients on exit. 
Update packer.go to cleanup plugin clients on exit. 

Since defer does not fire when exiting the application with os.Exit we need to be sure that we cleanup all of the clients on failures from the CLI and creating a new environment object.

atlassian/packer,youhong316/packer,tas50/packer,jen20/packer,jamesbishopp/packer,Sheile/packer,jsoriano/packer,hazelesque/packer,dayglojesus/packer,mohae/packer,monkeylittleinc/packer,visioncritical/packer,leroux/packer,marklap/packer,tracyde/packer,DualSpark/packer,dragon788/packer,quantang/packer,grubernaut/packer,bensojona/packer,grubernaut/packer,evertrue/packer,mwhooker/packer,pieter-lazzaro/packer,jonathankarsh/packer,samdunne/packer,markpeek/packer,yoctocloud/packer,jean/packer,zhuzhih2017/packer,jean/packer,monkeylittleinc/packer,bhcleek/packer,marc-ta/packer,LinusU/packer,atlassian/packer,blairham/packer,taliesins/packer,pieter-lazzaro/packer,dev-head/packer,uber/packer,hazelesque/packer,jamesleech/packer,jae2/packer,bryson/packer,pecigonzalo/packer,bhcleek/packer,cyberhouse/packer,israelshirk/packer,danschaffer/packer,grubernaut/packer,taliesins/packer,bryson/packer,life360/packer,paulmey/packer,rrva/packer,rickard-von-essen/packer,boumenot/packer,tb3088/packer,gbarberi/packer,manicai/packer,KohlsTechnology/packer,routelastresort/packer,hazelesque/packer,dantran/packer,ephemeralsnow/packer,trumant/packer,aneeshusa/packer,dragon788/packer,sequenceiq/packer,rickard-von-essen/packer,btd/packer,samdunne/packer,p1-nico/packer,pieter-lazzaro/packer,bryson/packer,btd/packer,tracyde/packer,tomwilkie/packer,mansunkuo/packer,c22/packer,ChrisLundquist/packer,yonglehou/packer,zeliff/packer,samdunne/packer,israelshirk/packer,masbog/packer,mvanholsteijn/packer,mefellows/packer,danschaffer/packer,rodm/packer,Banno/packer,tas50/packer,atlassian/packer,rrva/packer,visioncritical/packer,taliesins/packer,bhcleek/packer,life360/packer,jarl-dk/packer,burnzy/packer,paulvollmer/packer,kgrvamsi/packer,kpettijohn/packer,KFishner/packer,jszwedko/packer,higebu/packer,justincampbell/packer,rk295/packer,sean-/packer,jgkim/packer,pecigonzalo/packer,esemplare/packer,cyberhouse/packer,zakuro9715/packer,sean-/packer,tas50/packer,routelastresort/packer,Xiol/packer,jgkim/packer,grubernaut/packer,arizvisa/packer,monkeylittleinc/packer,pvanbuijtene/packer,p1-nico/packer,jonathankarsh/packer,KFishner/packer,dave2/packer,jasonchaffee/packer,oliviertremblay/packer,dieu/packer,aneeshusa/packer,trumant/packer,pearkes/packer,timsutton/packer,atlassian/packer,paulmey/packer,KohlsTechnology/packer,monsterzz/packer,ricardclau/packer,esemplare/packer,uber/packer,paulmey/packer,jasonchaffee/packer,LinusU/packer,dayglojesus/packer,pieter-lazzaro/packer,LinusU/packer,sgirones/packer,Silver90/packer,ephemeralsnow/packer,pieter-lazzaro/packer,Akasurde/packer,ricardclau/packer,mvanholsteijn/packer,feateds/packer,routelastresort/packer,ChrisLundquist/packer,zhuzhih2017/packer,henrysher/packer,beni55/packer,AlphaStaxLLC/packer,lantrix/packer,dantran/packer,higebu/packer,sansb/packer,rk295/packer,lantrix/packer,fnoeding/packer,sneal/packer,paulvollmer/packer,mitchellh/packer,lantrix/packer,mkuzmin/packer,jsternberg/packer,zhuzhih2017/packer,ttaylor249/packer,marc-ta/packer,icnocop/packer,smaato/packer,p1-nico/packer,jsoriano/packer,pvanbuijtene/packer,israelshirk/packer,dragon788/packer,rk295/packer,gbarberi/packer,aneeshusa/packer,zhuzhih2017/packer,avldya/packer,sean-/packer,zeliff/packer,dev-head/packer,youhong316/packer,sgirones/packer,jmptrader/packer,rickard-von-essen/packer,manicai/packer,feateds/packer,hazelesque/packer,kgrvamsi/packer,Silver90/packer,mvanholsteijn/packer,paulmey/packer,dave2/packer,shaunduncan/packer,ephemeralsnow/packer,icnocop/packer,dev-head/packer,oliviertremblay/packer,mefellows/packer,dragon788/packer,marc-ta/packer,yonglehou/packer,gildas/packer-hyperv,jamesleech/packer,gbarberi/packer,smaato/packer,manicai/packer,btd/packer,sobrinho/packer,quantang/packer,feateds/packer,legal90/packer,tb3088/packer,rnaveiras/packer,jamesbishopp/packer,KFishner/packer,dieu/packer,gildas/packer-hyperv,qur/packer,Sheile/packer,atlassian/packer,mafrosis/packer,jen20/packer,atlassian/packer,qur/packer,tsmolka/packer,ldejager/packer,jonathankarsh/packer,mgk/packer,gbarberi/packer,timsutton/packer,legal90/packer,tb3088/packer,sean-/packer,dantran/packer,Banno/packer,yoctocloud/packer,monkeylittleinc/packer,styro/packer,pieter-lazzaro/packer,mwhooker/packer,eranchetz/packer,cyberhouse/packer,smaato/packer,markpeek/packer,Silver90/packer,oliviertremblay/packer,jmptrader/packer,ttaylor249/packer,bhcleek/packer,napramirez/packer,vtolstov/packer,umang1912/packer,ricardclau/packer,leroux/packer,mayflower/packer,grubernaut/packer,styro/packer,mansunkuo/packer,qur/packer,sneal/packer,icnocop/packer,mgk/packer,mansunkuo/packer,bryson/packer,napramirez/packer,fnoeding/packer,orivej/packer,israelshirk/packer,KohlsTechnology/packer,jszwedko/packer,ttaylor249/packer,mafrosis/packer,tas50/packer,pvandervelde/packer,timsutton/packer,mohae/packer,dayglojesus/packer,BayanGroup/packer,zhuzhih2017/packer,boumenot/packer,ldejager/packer,rickard-von-essen/packer,yonglehou/packer,yoctocloud/packer,ChrisLundquist/packer,jen20/packer,eranchetz/packer,kgrvamsi/packer,bensojona/packer,evertrue/packer,mefellows/packer,kpettijohn/packer,ChrisLundquist/packer,tsmolka/packer,pearkes/packer,justincampbell/packer,bradparks/packer__create_vm_for_aws_docker_vagrant_etc,esemplare/packer,mafrosis/packer,jae2/packer,taliesins/packer,samdunne/packer,icnocop/packer,samdunne/packer,fnoeding/packer,noplay/packer,threatstream/packer,umang1912/packer,manicai/packer,sansb/packer,mayflower/packer,ttaylor249/packer,pvandervelde/packer,bensojona/packer,vtolstov/packer,icnocop/packer,markpeek/packer,BayanGroup/packer,c22/packer,monsterzz/packer,routelastresort/packer,noplay/packer,noplay/packer,justincampbell/packer,routelastresort/packer,sequenceiq/packer,BayanGroup/packer,taliesins/packer,c22/packer,pearkes/packer,dave2/packer,blairham/packer,monkeylittleinc/packer,styro/packer,mwhooker/packer,mitchellh/packer,leroux/packer,AlphaStaxLLC/packer,burnzy/packer,grange74/packer,eranchetz/packer,tsmolka/packer,mafrosis/packer,sansb/packer,jen20/packer,legal90/packer,jszwedko/packer,danschaffer/packer,zeliff/packer,tomwilkie/packer,danschaffer/packer,bensojona/packer,shaunduncan/packer,mansunkuo/packer,tsmolka/packer,jarl-dk/packer,umang1912/packer,DualSpark/packer,pecigonzalo/packer,Cbeck527/packer,boumenot/packer,stagrlee/packer,jimmythedog/packer,pvandervelde/packer,shaunduncan/packer,pvandervelde/packer,Xiol/packer,mgk/packer,dave2/packer,markpeek/packer,rnaveiras/packer,jgkim/packer,hashicorp/packer,napramirez/packer,stagrlee/packer,legal90/packer,mayflower/packer,beni55/packer,marklap/packer,sneal/packer,hasJackb/packer,paulmey/packer,fnoeding/packer,tas50/packer,grubernaut/packer,ttaylor249/packer,zakuro9715/packer,ephemeralsnow/packer,mefellows/packer,jamesleech/packer,blairham/packer,esemplare/packer,jarl-dk/packer,dieu/packer,DualSpark/packer,bradparks/packer__create_vm_for_aws_docker_vagrant_etc,timsutton/packer,threatstream/packer,evertrue/packer,rnaveiras/packer,grange74/packer,jsoriano/packer,ChrisLundquist/packer,mitchellh/packer,henrysher/packer,jgkim/packer,stagrlee/packer,BayanGroup/packer,ldejager/packer,grange74/packer,trumant/packer,p1-nico/packer,rnaveiras/packer,avldya/packer,ricardclau/packer,threatstream/packer,tb3088/packer,sobrinho/packer,uber/packer,jszwedko/packer,ober/packer,jsoriano/packer,jamesbishopp/packer,youhong316/packer,tomwilkie/packer,markpeek/packer,quantang/packer,hashicorp/packer,henrysher/packer,jmptrader/packer,smaato/packer,aneeshusa/packer,pvandervelde/packer,lantrix/packer,visioncritical/packer,jae2/packer,mkuzmin/packer,stagrlee/packer,youhong316/packer,mwhooker/packer,orivej/packer,orivej/packer,trumant/packer,bryson/packer,beni55/packer,rk295/packer,zeliff/packer,sansb/packer,ricardclau/packer,orivej/packer,smaato/packer,dantran/packer,ephemeralsnow/packer,yoctocloud/packer,vtolstov/packer,styro/packer,Banno/packer,yonglehou/packer,c22/packer,tracyde/packer,dayglojesus/packer,bradparks/packer__create_vm_for_aws_docker_vagrant_etc,avldya/packer,cyberhouse/packer,qur/packer,bradparks/packer__create_vm_for_aws_docker_vagrant_etc,jean/packer,mayflower/packer,avldya/packer,Akasurde/packer,rodm/packer,sean-/packer,ober/packer,zakuro9715/packer,DualSpark/packer,jmptrader/packer,mafrosis/packer,rrva/packer,mansunkuo/packer,gildas/packer-hyperv,mayflower/packer,tb3088/packer,sgirones/packer,quantang/packer,tracyde/packer,rnaveiras/packer,rickard-von-essen/packer,mohae/packer,zhuzhih2017/packer,dantran/packer,rnaveiras/packer,noplay/packer,arizvisa/packer,umang1912/packer,tsmolka/packer,c22/packer,p1-nico/packer,hashicorp/packer,jen20/packer,tas50/packer,grange74/packer,c22/packer,markpeek/packer,hasJackb/packer,kgrvamsi/packer,taliesins/packer,yoctocloud/packer,marklap/packer,boumenot/packer,mkuzmin/packer,uber/packer,pvanbuijtene/packer,esemplare/packer,KFishner/packer,burnzy/packer,youhong316/packer,tb3088/packer,jean/packer,masbog/packer,kpettijohn/packer,vtolstov/packer,tsmolka/packer,Akasurde/packer,sequenceiq/packer,Cbeck527/packer,rrva/packer,pvanbuijtene/packer,mohae/packer,life360/packer,leroux/packer,btd/packer,mohae/packer,jasonchaffee/packer,Cbeck527/packer,mitchellh/packer,p1-nico/packer,blairham/packer,jsternberg/packer,LinusU/packer,jsternberg/packer,mindjiver/packer,Cbeck527/packer,danschaffer/packer,pearkes/packer,mkuzmin/packer,sneal/packer,jonathankarsh/packer,grange74/packer,feateds/packer,mkuzmin/packer,mwhooker/packer,mindjiver/packer,Cbeck527/packer,henrysher/packer,dave2/packer,rodm/packer,napramirez/packer,jsternberg/packer,sneal/packer,bryson/packer,mkuzmin/packer,jamesleech/packer,life360/packer,rodm/packer,AlphaStaxLLC/packer,hasJackb/packer,arizvisa/packer,mindjiver/packer,boumenot/packer,jasonchaffee/packer,threatstream/packer,hasJackb/packer,jimmythedog/packer,shaunduncan/packer,visioncritical/packer,arizvisa/packer,dev-head/packer,sequenceiq/packer,gildas/packer-hyperv,paulvollmer/packer,Akasurde/packer,ricardclau/packer,Xiol/packer,legal90/packer,KohlsTechnology/packer,jamesbishopp/packer,hashicorp/packer,mindjiver/packer,jarl-dk/packer,bhcleek/packer,justincampbell/packer,vtolstov/packer,higebu/packer,timsutton/packer,masbog/packer,dayglojesus/packer,smaato/packer,monsterzz/packer,zakuro9715/packer,kpettijohn/packer,jasonchaffee/packer,threatstream/packer,paulvollmer/packer,jen20/packer,KohlsTechnology/packer,jimmythedog/packer,pecigonzalo/packer,jae2/packer,dieu/packer,paulmey/packer,arizvisa/packer,KohlsTechnology/packer,timsutton/packer,beni55/packer,marc-ta/packer,sobrinho/packer,ober/packer,higebu/packer,Akasurde/packer,dave2/packer,Sheile/packer,pvanbuijtene/packer,evertrue/packer,oliviertremblay/packer,eranchetz/packer,arizvisa/packer,jimmythedog/packer,mvanholsteijn/packer,sean-/packer,burnzy/packer,ober/packer,Silver90/packer,Sheile/packer,monsterzz/packer,AlphaStaxLLC/packer,ChrisLundquist/packer,mitchellh/packer,marklap/packer,masbog/packer,life360/packer,mgk/packer,ober/packer,youhong316/packer,ldejager/packer,Xiol/packer,higebu/packer,jimmythedog/packer,sgirones/packer,sobrinho/packer,tomwilkie/packer,quantang/packer,pvandervelde/packer