Fix hostnames for admin virtual IPs

Because of a wrong check, we are always creating "admin.$foo" hostnames
for virtual IPs in the admin network, while this should really be just
"$foo".
Merge pull request #93 from vuntz/vip-hostname

Fix hostnames for admin virtual IPs
Merge branch 'release/roxy/master' into roxy-sync
Merge pull request #94 from vuntz/roxy-sync

Merge roxy branch into stoney