xenapi: Uninstall instances
xenapi: Uninstall instances

The devstack script sometimes failed to clean up the left over
instances. This patch will utilize the xe vm-uninstall force=true
command to get rid of the instances.

Change-Id: I3450e2d5c9a4b1fe8ede39c4cc5c337cd541ea35

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