monitor_reconfig: Add script to run for external displays.

This adds a run_monitor_configure script that uses xrandr to
check if there's an external display connected, and then
runs monitor_reconfigure if so.  I plan to make us run this
after starting the X server.

Change-Id: Ia19b5832950e405d9d88295226771d6364846b99

TEST=ran it

Review URL:
1 file changed