Add option not to run bash after execing stack.sh
Add option not to run bash after execing stack.sh

If stack.sh is run as root, it execs stack.sh as stack, but also
runs bash after doing so to provide a prompt as the stack user.

In unattended installations this isn't desired as it will prevent
the original job from completing.

This change adds a paremeter "SHELL_AFTER_RUN" which can be set
to "no" to prevent the final invocation of bash.

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