ALLJOYN-2055 The SessionListener now includes the reason a session is lost

The SessionLost callback now sends the reason that the session was lost when
the session lost callback is sent.

Small modification made when creating the alljoyn_busobject. When creating an
alljoyn_busobject if none of the callbacks are needed you would still have to
create an alljoyn_buobject_callbacks struct all of the callbacks set to NULL.
If no callbacks are needed NULL can be passed in as the
alljoyn_busobject_callbacks and the callback values will be set properly now.

changed some global values in SessionTest to static global values so that the
values would not be seen in other unit tests.

New set of unit tests added to test the changes to the SessionListener.

Change-Id: Ifad7f853217b71b957eaebaefeb01d25fa157acf