mgr/cephadm: allow mgr colo if mgr_standby_modules=false

mgr/cephadm: allow mgr colo if mgr_standby_modules=false

If the standby mgr daemons' modules aren't listening on any ports, then we
can schedule multiple on the same host.

Note that this may make 'orch ps' output misleading, as ports will be
reported for each mgr instance, but only one of them will actually be
listening at any one time (if they are behaving, at least!).  Treat a
mgr port check error as non-fatal.

Signed-off-by: Sage Weil <sage@newdream.net>