engine.py.in: adding note about setting password

Users should be warn that if they set password to be able to add
oVirt Node from oVirt Engine it will enable SSH daemon.

Change-Id: Ibb0d6e590188165d7cb92aaa5a73b7713f3b522b
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=746582
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/13267
Reviewed-by: Dan Kenigsberg <danken@redhat.com>