Remove docker exercise
Remove docker exercise

No other hypervisor has a dedicated exercise, docker should be
tested just by testing the nova APIs, not on it's own.

Change-Id: Ifc788815380e8502449171410dea8260786a1e79

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