migration: Export tls-[creds|hostname|authz] params to cmdline too

It's useful for specifying tls credentials all in the cmdline (along with
the -object tls-creds-*), especially for debugging purpose.

The trick here is we must remember to not free these fields again in the
finalize() function of migration object, otherwise it'll cause double-free.

The thing is when destroying an object, we'll first destroy the properties
that bound to the object, then the object itself.  To be explicit, when
destroy the object in object_finalize() we have such sequence of
operations:

    object_property_del_all(obj);
    object_deinit(obj, ti);

So after this change the two fields are properly released already even
before reaching the finalize() function but in object_property_del_all(),
hence we don't need to free them anymore in finalize() or it's double-free.

This also fixes a trivial memory leak for tls-authz as we forgot to free it
before this patch.

Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20220707185515.27475-1-peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>