Rename doc environment to docs
Rename doc environment to docs

As per the governance resolution https://review.openstack.org/119875,
projects should have a docs environment in their tox.ini testing
interface. Rename the doc environment to docs.

Change-Id: Ie7c685c3af1abc480bcd7cf3d54e018ad74081a4

yeming233/rally,paboldin/rally,shdowofdeath/rally,aplanas/rally,aforalee/RRally,gluke77/rally,amit0701/rally,eayunstack/rally,shdowofdeath/rally,gluke77/rally,vefimova/rally,eayunstack/rally,pandeyop/rally,cernops/rally,vponomaryov/rally,varunarya10/rally,pandeyop/rally,eonpatapon/rally,yeming233/rally,redhat-openstack/rally,vganapath/rally,paboldin/rally,vefimova/rally,eayunstack/rally,pyKun/rally,openstack/rally,openstack/rally,aplanas/rally,go-bears/rally,cernops/rally,afaheem88/rally,vganapath/rally,go-bears/rally,group-policy/rally,openstack/rally,group-policy/rally,pyKun/rally,aforalee/RRally,vganapath/rally,gluke77/rally,amit0701/rally,redhat-openstack/rally,varunarya10/rally,amit0701/rally,vganapath/rally,afaheem88/rally,openstack/rally,eonpatapon/rally,group-policy/rally,vponomaryov/rally,gluke77/rally,paboldin/rally