Support configurable mysql host in gerrit

In further support of using a trove db, remove the gerrit::mysql
module from review-dev.  Plumb mysql_host throughout and remove
the no longer necessary mysql_root_password.  Configure review-dev
to use mysql_host from hiera, but configure review to use
'localhost'.

Change-Id: Id13cea66601f80c5b17d2a4069a14f7b458ea09d