labs: rename openstackrc file

Rename labs-openstackrc.sh to admin-openstackrc.sh because we are about
to introduce a second openstackrc.sh for a user that is obviously also
part of labs, but not an admin.

Change-Id: Ifa58b260e7b5386ce7ccc6075cdf5ef2dc1ee9ce
Merge "labs: rename openstackrc file"