Atom: ScheduledJobStateChanged

Rename the possible states in ScheduleJobStateChanged
from ON and OFF to SCHEDULED, STARTED, and FINISHED.
Added the log line in JobSchedulerService for SCHEDULE.
STARTED corresponds to what previously was the ON event.
FINISHED corresponds to what previously was the OFF event.

Test: accompanying CTS test
Change-Id: I779dd58092e8fdee58561b8e8e74be5404f3ed93
diff --git a/stats/atoms.proto b/stats/atoms.proto
index 4a7f0c4..cc98b98 100644
--- a/stats/atoms.proto
+++ b/stats/atoms.proto
@@ -322,8 +322,9 @@
     optional string name = 2;
 
     enum State {
-        OFF = 0;
-        ON = 1;
+        FINISHED = 0;
+        STARTED = 1;
+        SCHEDULED = 2;
     }
     optional State state = 3;