Split bugreport identifier into id and pid.

Although 'pid' is more useful when diagnosing problems with the
bugreport workflow, it could be confusing to the end user. Hence, a
sequential id (started at 1 after a reboot) would be more useful, and this CL changes Shell to accommodate such id (dumpstate will be changed separately).

BUG: 27076108
Change-Id: I5c42dc49a100b43266787d4f79698a22a4e533a9