Notify video capability to listeners in certain new scenarios

- In certain cases, we have seen that when the phone
  object is deleted/re-created, we fail to notify the
  video capability to the listeners.

- There also seemed to be a race condition when the
  time a listener registers is not in sync with
  the time we are notified of the video capability.

- In order to fix the above two issues, we notify
  registrants when a new phone is created and
  updateParentPhone is called. Also, when a new
  registrant registers with us for video capability
  changed, we immediately notify them of our cached
  capability.

Change-Id: Ic6002c2518104c20b5de10d1081af4559f506ace
CRs-Fixed: 753845