Fix allowing playback capture for packages with shared UID

Use getPackagesForUid in place of getNamesForUids to retrieve the
list of packages for a certain UID.
In case of shared UIDs, getNamesForUids does not return the list
of packages belonging to the UID, but just a single item in the
form "shared:<sharedUserId>", which causes isAudioPlaybackCaptureAllowed
to always return false.

Change-Id: I0da61945e17d013c3c7a5633f231dbfb8f06b248