metrics: Add a CLI flag to disable dbus.

DBus is not setup in several targets and the metrics_daemon will crash
if it cannot connect to DBus.
Running metrics daemon without dbus allows us to test the daemon in any
target.

BUG: 22879597

Change-Id: Ica69c8e96c3df794a210a0fa3d44f85a98a660f0
3 files changed