bootstat: reduce overall boot time

Run bootstat as a oneshot service rather than as a series of inline
exec commands.  exec commands impact boot time.

Test: cts-tradefed run cts-dev --module CtsBootStatsTestCases
      system/core/bootstat/boot_reason_test.sh all
         (make sure it filters out new init reports)
Bug: 65736247
Change-Id: Ic9d509a8cbee4bc1e278081de1001e25ae0915fd
diff --git a/bootstat/boot_reason_test.sh b/bootstat/boot_reason_test.sh
index 6d2f5d7..4314271 100755
--- a/bootstat/boot_reason_test.sh
+++ b/bootstat/boot_reason_test.sh
@@ -176,6 +176,8 @@
 init    : processing action (boot) from (/system/etc/init/bootstat.rc
 init    : processing action (ro.boot.bootreason=*) from (/system/etc/init/bootstat.rc
 init    : processing action (sys.boot_completed=1 && sys.logbootcomplete=1) from (/system/etc/init/bootstat.rc
+ (/system/bin/bootstat --record_boot_complete --record_boot_reason --record_time_since_factory_reset -l)'
+ (/system/bin/bootstat -r post_decrypt_time_elapsed)'
 init    : Command 'exec - system log -- /system/bin/bootstat --record_boot_complete' action=sys.boot_completed=1 && sys.logbootcomplete=1 (/system/etc/init/bootstat.rc:
 init    : Command 'exec - system log -- /system/bin/bootstat --record_boot_reason' action=sys.boot_completed=1 && sys.logbootcomplete=1 (/system/etc/init/bootstat.rc:
 init    : Command 'exec - system log -- /system/bin/bootstat --record_time_since_factory_reset' action=sys.boot_completed=1 && sys.logbootcomplete=1 (/system/etc/init/bootstat.rc: