schema: document the launchPaused parameter

add documentation for the launchPaused param,
which was missing from the API schema.

Change-Id: I279e68c7e6b2cca8496a5dbec6e3895d531bce97
Signed-off-by: Francesco Romani <fromani@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/24144
Reviewed-by: Dan Kenigsberg <danken@redhat.com>