Fix a race condition in NativeDaemonConnector

Fixes a race between the onDaemonConnected callback and setting the
mOutputStream in NativeDaemonConnector.

MountService connects to vold using the NativeDaemonConnector.
Throws a “NativeDaemonConnectorException: No output stream!”
when the onDaemonConnected callback in MountService calls the doListCommand.

Change-Id: Ib895bab37f7df680e4362df6366198c0a673c5e9