Clean up cinder volume group rather than remove it
Clean up cinder volume group rather than remove it

Removing the cinder volume group breaks devstack installations
that share that volume group with other logical volumes. It also was
leaking loopback devices.

Change-Id: Ice4470e06e08ce49a0e1f82af70abcc015c91c20

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