Ensure conference state is posted to Telecom for new conferences.

There is an edge-case where an IMS conference fails to merge two
participants into a conference, AND the conference event package comes in
before the ImsCall indicates it is multiparty.  In this case, the CEP
will have a single participant which means we'll treat the call as a
standalone call.  ImsConference correctly sets the conference state, but
this was previously just passed along the ConnectionService adapter
to Telecom.  In this case the conference isn't even added to Telecom so
the method call in effect does nothing.

Changed to cache the conference state and ensure when adding the conference
to Telecom that we call the setConferenceState method (yeah, could have
put this in the ParcelableConference, but this is an edge case).

Test: Wrote unit test to verify property is set.
Bug: 134047008
Fixes: 155097934
Merged-In: I203880c593f6bac471a06eb9dcbb529d0bb75ba5
Change-Id: Ib48437abb1295d147e227727ce4ff2996f28b5de