Add runtime restart information to sysprops and eventlog

Added 3 more system props:
- sys.system_server.start_count
How many times the system server has started, 1-based.

- sys.system_server.start_elapsed
Elapsed time when the system server started most recently

- sys.system_server.start_uptime
Uptime when the system server started most recently

Also log the same information on event log, as 'system_server_start'.

Bug: 124022170
Test: manual
$ adb logcat -b events -s system_server_start
02-15 23:35:06.151  1222  1222 I system_server_start: [1,4714,4714]
 (killed the system server)
02-15 23:35:24.673  4209  4209 I system_server_start: [2,23236,23236]

$ getprop | grep system_server
[sys.system_server.start_count]: [2]
[sys.system_server.start_elapsed]: [23236]
[sys.system_server.start_uptime]: [23236]

Change-Id: Ie3e77903e723eb5b7e79b545d4287d9b07c4b379