Update multiple backend configuration in tempest script
Update multiple backend configuration in tempest script

Currently when we configure the tempest with multiple LVM
backends the backend names are created as LVM_iSCSI and
LVM_iSCSI_2 which fails since the backends created by cinder
are lvmdriver-1 and lvmdriver-2.

This patch updates the backend names. Added support for
CINDER_ENABLED_BACKENDS and added todo to remove
CINDER_MULTI_LVM_BACKEND once its formally removed

Closes-Bug:#1369946
Closes-Bug:#1369942

Change-Id: If44f5eb206616afb0fbaf333f3fa6a296d4650cd

eharney/devstack,ozamiatin/devstack,affo/devstack,pacinete/devstack,varunarya10/devstack,pacinete/devstack,eharney/devstack,CloudServer/devstack,vishnugonela/devstack,Mahito/devstack,upadhyay-prashant/devstack,CloudServer/devstack,olivierlemasle/devstack,LoHChina/devstack,group-policy/devstack,openstack-dev/devstack,pczerkas/devstack,costingalan/devstack,bq-xiao/devstack,bljgaurav/openstack-test,LoHChina/devstack,liuquansheng47/devstack,BSJAIN92/OpenStack,atulpatil301/devstack,HPCHub/devstack,ozamiatin/devstack,dtroyer/devstack,neerja28/Devstack_GlusterFS,Mahito/devstack,sc68cal/devstack,thomasem/devstack,TwinkleChawla/devstack,bigswitch/devstack,neerja28/Devstack_GlusterFS,andrewrothstein/devstack,noironetworks/devstack,pombredanne/devstack,avvocatodemarchis/devstack,group-policy/devstack,rushiagr/devstack,NaokiMiyata/devstack,dirkmueller/devstack,varunarya10/devstack,openstack-dev/devstack,kplus/devstack-moonshot,mssumanth/devstack,prithivm/branch01,dtroyer/devstack,promptworks/devstack,sequenceiq/devstack,samgoon/devstack,j4/devstack,mssumanth/devstack,bq-xiao/devstack,rushiagr/devstack,nuxeh/devstack,vsham20/devstack,HPCHub/devstack,parul24/devstack,bswartz/devstack,andrewrothstein/devstack,kplus/devstack-moonshot,sequenceiq/devstack,wenhuizhang/devstack,j4/devstack,flavio-fernandes/devstack,mc2014/devstack,vsham20/devstack,bigswitch/devstack,promptworks/devstack,costingalan/devstack,nuxeh/devstack,mc2014/devstack,parul24/devstack,pombredanne/devstack,TwinkleChawla/devstack,bswartz/devstack,nawawi/openstack,thomasem/devstack,atulpatil301/devstack,noironetworks/devstack,nawawi/openstack,flavio-fernandes/devstack,dirkmueller/devstack,liuquansheng47/devstack,herrsechs/devstack,upadhyay-prashant/devstack,avvocatodemarchis/devstack,affo/devstack,sc68cal/devstack,richliu/devstack,mmasaki/devstack,olivierlemasle/devstack,herrsechs/devstack,vishnugonela/devstack,mmasaki/devstack,NaokiMiyata/devstack,bljgaurav/openstack-test,samgoon/devstack,richliu/devstack,pczerkas/devstack,BSJAIN92/OpenStack,prithivm/branch01,wenhuizhang/devstack