Atom: BootSequenceReported

Logs information about boot time and reason to statsd.
Specifically: bootloader boot reason, system boot reason, bootloader
boot time, total boot time, time that the boot finished, and time since
last boot.

Test: booted the phone and verified "adb logcat -b stats" received the
event

Change-Id: I769df9a09263ed3667f7085c81b3d072e868cbda