Use correct variable for host_access dependency

The keystone::db::mysql resource declares resources using
`$real_allowed_hosts` which is a copy of `$allowed_hosts` minus `$host`.
But then it declares dependencies using `$allowed_hosts` which includes
`$host` and will fail catalog compilation due to a missing dependency

This bug only affects users if the value of `$host` is included in the
array of `$allowed_hosts`

Change-Id: Ifdd8793bcf36178efd1a083ee35649d56dc3d768
(cherry picked from commit 7813820abd30e77c6119e11d390237c1e6978086)