api: Separate api schema into its own package

The vdsm schema definition is needed by the vdsm server but also by clients.
Split the shema into its own package so it can be installed by clients without
pulling in server-side dependencies.

Change-Id: I6ae8d6e57c11bf89d6c695df7cf80b436495069e
Signed-off-by: Adam Litke <agl@us.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/11864
Reviewed-by: Saggi Mizrahi <smizrahi@redhat.com>