apps: Use transition line as initial service state

shill logs often start with the system actively running.  When in this
state, it is not sufficient to assume the first service state update was
the state of the service from the start of the log.  Instead, the log
processor attempts to use an alternate log line to detect what the
previous state was.  If the alternate line is the first service state
log line detected, this hint is assumed to be the service state from the
start of the log.

TEST=ran "grunt test" and manually checked multiple shill logs

Change-Id: I135e0ab74f31947376901ffdda712a5572c1c56b
3 files changed