support memcache for keystone token backend
support memcache for keystone token backend

Change-Id: I0c85a64932c39264b73cff4f9d952d0dbdf49e5b

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