tools: Sort domains when validating in engine-manage-domains

Sort domains by name prior to validate action in engine-manage-domains.

Change-Id: I6243fb8d6ae1fc34c31517559bb56b091cc10b1d
Bug-Url: https://bugzilla.redhat.com/1057182
Signed-off-by: Martin Perina <mperina@redhat.com>