Merge "bootstat: Calculate and log the time_since_last_boot metric."
am: 1607ea6

* commit '1607ea64cbdeea766c05d033afe0c65ea978b399':
  bootstat: Calculate and log the time_since_last_boot metric.

Change-Id: I643c0847a75e4ba02db17ea5e4c716f6fcc7b28d