Lower default IRONIC_VM_SPECS_RAM
Lower default IRONIC_VM_SPECS_RAM

Revert the default required RAM for Ironic nodes from 1024MB to 512MB.
Ironic now passes a kernel parameter to deploy ramdisks that avoids use
of tmpfs and lowers minimum memory requirements.

Change-Id: I20226c496fdd06ecfc6769a60b6d6f82887130a8

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