Set MYSQL_HOST parameter to better support multi-node mode.
Set MYSQL_HOST parameter to better support multi-node mode.

When deploying openstack with multi-node mode,
mysql needs to be started by listening it's real ip, not localhost.
but devstack always use localhost to recreate databases that will
lead bellow errors.

Fix bug 1177735

Change-Id: I50284f469a998d023a41b4796f1dc775bb52e710

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