Fix document about Rally with DevStack all-in-one installation
Fix document about Rally with DevStack all-in-one installation

The document about 'Rally with DevStack all-in-one installation'
shows that DevStack uses `localrc`, however DevStack uses `local.conf` now.
This patch fix (`localrc`->`local.conf`) the document.

Change-Id: I8fc707b6d30b2ebbe2643f9eba0b01d8bda817cb
Closes-bug: 1460582

shdowofdeath/rally,vganapath/rally,pyKun/rally,yeming233/rally,openstack/rally,group-policy/rally,aplanas/rally,redhat-openstack/rally,amit0701/rally,eayunstack/rally,go-bears/rally,redhat-openstack/rally,eonpatapon/rally,afaheem88/rally,vponomaryov/rally,aforalee/RRally,gluke77/rally,gluke77/rally,vefimova/rally,paboldin/rally,amit0701/rally,afaheem88/rally,gluke77/rally,aplanas/rally,gluke77/rally,go-bears/rally,shdowofdeath/rally,pyKun/rally,eayunstack/rally,eayunstack/rally,amit0701/rally,openstack/rally,openstack/rally,yeming233/rally,paboldin/rally,group-policy/rally,openstack/rally,vganapath/rally,vefimova/rally,vganapath/rally,cernops/rally,paboldin/rally,aforalee/RRally,vganapath/rally,cernops/rally,eonpatapon/rally,vponomaryov/rally,group-policy/rally