Fix issue with ml2 plugin on using provider network
Fix issue with ml2 plugin on using provider network

This commit fixes the issue that ml2 plugin
sets 'flat_networks' in ml2 configuration file as
empty.  The value of 'flat_networks' need to be set 
as the name of the physical network that was specified 
in the localrc file (or it's default value).

Change-Id: Ib4c31f6576da57534b36aefebd1ca8cd397c6c1a

upadhyay-prashant/devstack,pombredanne/devstack,pczerkas/devstack,olivierlemasle/devstack,j4/devstack,CloudServer/devstack,avvocatodemarchis/devstack,dirkmueller/devstack,parul24/devstack,flavio-fernandes/devstack,rushiagr/devstack,bswartz/devstack,herrsechs/devstack,eharney/devstack,dirkmueller/devstack,vsham20/devstack,bigswitch/devstack,flavio-fernandes/devstack,LoHChina/devstack,dtroyer/devstack,bq-xiao/devstack,bq-xiao/devstack,LoHChina/devstack,openstack-dev/devstack,richliu/devstack,upadhyay-prashant/devstack,group-policy/devstack,bigswitch/devstack,nawawi/openstack,prithivm/branch01,nawawi/openstack,mssumanth/devstack,dtroyer/devstack,bljgaurav/openstack-test,j4/devstack,Mahito/devstack,ozamiatin/devstack,NaokiMiyata/devstack,pacinete/devstack,ozamiatin/devstack,herrsechs/devstack,bljgaurav/openstack-test,pczerkas/devstack,HPCHub/devstack,costingalan/devstack,eharney/devstack,mc2014/devstack,atulpatil301/devstack,richliu/devstack,TwinkleChawla/devstack,NaokiMiyata/devstack,group-policy/devstack,pacinete/devstack,parul24/devstack,atulpatil301/devstack,mc2014/devstack,wenhuizhang/devstack,varunarya10/devstack,liuquansheng47/devstack,olivierlemasle/devstack,openstack-dev/devstack,prithivm/branch01,HPCHub/devstack,noironetworks/devstack,Mahito/devstack,costingalan/devstack,samgoon/devstack,andrewrothstein/devstack,samgoon/devstack,vishnugonela/devstack,noironetworks/devstack,pombredanne/devstack,wenhuizhang/devstack,bswartz/devstack,mssumanth/devstack,mmasaki/devstack,rushiagr/devstack,liuquansheng47/devstack,vishnugonela/devstack,vsham20/devstack,CloudServer/devstack,mmasaki/devstack,thomasem/devstack,thomasem/devstack,avvocatodemarchis/devstack,varunarya10/devstack,TwinkleChawla/devstack,andrewrothstein/devstack