client, broker: method to read agent metadata without broker

Provide a method usable by the ha setup application which will read and
parse the ha metadata from the domain without requiring the ha broker.

The initial planned use for this is to have setup verify host_id
uniqueness during setup before starting the ha daemons.

Change-Id: I51612715eee18a488e7d1f7942f0891e35b1fc62
Bug-Url: https://bugzilla.redhat.com/1012417
Signed-off-by: Greg Padgett <gpadgett@redhat.com>