Fix race condition in AwesomePlayer

This fixes a race condition that could cause two threads to attempt to
connect to a server at the same time, resulting in multiple requests
and/or aborted connections. In some cases, it could cause other operations
on MediaPlayer to block until network access was complete.

b/13187722

Change-Id: Ibf78acff15dbfbf6c443a4c60623e8eac967d955