add non-interactive flags to apt.
add non-interactive flags to apt.

This replaces 'apt-get' calls with 'apt_get' function that just
ensures that each call has flags to be non-interactive.  This prevents
potential prompts for conf file overwrites and such.

upadhyay-prashant/devstack,williamthegrey/devstack,atulpatil301/devstack,nuxeh/devstack,dirkmueller/devstack,citrix-openstack-build/devstack,nati/devstack_public,pacinete/devstack,wenhuizhang/devstack,noironetworks/devstack,shootstar/devstacktest,atulpatil301/devstack,citrix-openstack-build/devstack,jamielennox/devstack,mc2014/devstack,mmasaki/devstack,sstrato/devstack,bq-xiao/devstack,costingalan/devstack,ozamiatin/devstack,Juniper/devstack,vsham20/devstack,r-mibu/devstack,openstack-dev/devstack,Mahito/devstack,pczerkas/devstack,virtualopensystems/devstack,mssumanth/devstack,affo/devstack,eshnil2000/devstack,TwinkleChawla/devstack,olivierlemasle/devstack,j4/devstack,nawawi/openstack,HPCHub/devstack,prithivm/branch01,Yuriy-Leonov/devstack,mssumanth/devstack,ozamiatin/devstack,bigswitch/devstack,ykaneko/devstack,kplus/devstack-moonshot,r-mibu/devstack,nawawi/openstack,bljgaurav/openstack-test,ewindisch/raspi-devstack,BSJAIN92/OpenStack,bigswitch/devstack,neerja28/Devstack_GlusterFS,Millnert/contrail-devstack,olivierlemasle/devstack,costingalan/devstack,samgoon/devstack,j4/devstack,yamt/devstack,innodee/openstackk,sc68cal/devstack,tianweizhang/devstack,LoHChina/devstack,group-policy/devstack,richliu/devstack,rushiagr/devstack,nttmcl/devstack_public,group-policy/devstack,sc68cal/devstack,parul24/devstack,liuquansheng47/devstack,andrewrothstein/devstack,pombredanne/devstack,openstack-dev/devstack,tianweizhang/devstack,nttmcl/devstack_public,varunarya10/devstack,nuxeh/devstack,noironetworks/devstack,NaokiMiyata/devstack,kplus/devstack-moonshot,pacinete/devstack,dtroyer/devstack,avvocatodemarchis/devstack,HPCHub/devstack,prithivm/branch01,liuquansheng47/devstack,mmasaki/devstack,vishnugonela/devstack,varunarya10/devstack,savi-dev/devstack,thomasem/devstack,mc2014/devstack,eharney/devstack,promptworks/devstack,thomasem/devstack,TwinkleChawla/devstack,bswartz/devstack,CiscoSystems/devstack,promptworks/devstack,armando-migliaccio/devstack,Mahito/devstack,neerja28/Devstack_GlusterFS,inkerra/devstack,sequenceiq/devstack,herrsechs/devstack,bswartz/devstack,samgoon/devstack,flavio-fernandes/devstack,BSJAIN92/OpenStack,rushiagr/devstack,vishnugonela/devstack,eharney/devstack,dtroyer/devstack,herrsechs/devstack,bq-xiao/devstack,LoHChina/devstack,affo/devstack,parul24/devstack,NaokiMiyata/devstack,cloudbuilders/devstack,wenhuizhang/devstack,bljgaurav/openstack-test,pombredanne/devstack,pczerkas/devstack,flavio-fernandes/devstack,nati/devstack_public,sequenceiq/devstack,CloudServer/devstack,CloudServer/devstack,cloudbuilders/devstack,dirkmueller/devstack,richliu/devstack,upadhyay-prashant/devstack,ewindisch/raspi-devstack,savi-dev/devstack,andrewrothstein/devstack,srics/devstack,deepakselvaraj/devstack,vsham20/devstack,JioCloud/devstack,ykaneko/devstack,avvocatodemarchis/devstack