Keystore 2.0: Implement unique id rotation on factory reset.

This patch implements unique id rotation on factory reset. It is assumed
that the timestamp file disappears on factory reset so the timestamp
file's creation time gives a lower bound on the time since the last
factory reset.

Bug: 184784809
Test: atest keystore2_test
Change-Id: Iaa1c74b0ccffe69d5d9c68e7c6dac98a13136437
6 files changed