stasis_message.c: Don't create immutable stasis objects with locks.

* Create the stasis message object without a lock as it is immutable.
* Create the stasis message type object without a lock as it is immutable.
* Creating the stasis message type could crash if the passed in type name
is NULL and REF_DEBUG is enabled.  Added missing NULL check when passing
the ao2 object tag string.

Change-Id: I28763c58bb9f0b427c11971d0103bf94055e7b32