Reduce extra connections made to app

When new media data is loaded, update manager immediately, to avoid
extra unnecessary connections if the app sends more updates before we
can start the test connection.
Also improve connection handling in ResumeMediaBrowser to remove
redundant calls to disconnect

Test: atest MediaResumeListenerTest ResumeMediaBrowserTest
Fixes: 271211860
Change-Id: If2c7b9fe761c5b453f699fa3bfa5bb05436d1ac4