engine-manage-domains: Adding man page

Adding engine-manage-domains.8

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=742421
Change-Id: I26e69ce1410ce1ffd0c8ce242ea519ff3c5daee6
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>