Detect factory reset and deleteAllKeys

Where metadata encryption is enabled, if there is no metadata encryption
key present and we are generating one anew, then there has been a
factory reset, and this is the first key to be generated. We then call
deleteAllKeys to ensure data from before the factory reset is securely
deleted.

This shouldn't really be necessary; the factory reset call itself
should be doing this. However there are currently three factory reset
paths (settings, recovery, fastboot -w) and it is not clear that all
three are doing this correctly on all devices. Obviously an attacker
can prevent this code from being run by running a version of the OS
that does not include this change; however, if the bootloader is
locked, then keys will be version bound such that they will only work
on locked devices with a sufficiently recent version of the OS. If
every sufficiently recent signed version of the OS includes this change
the attack is defeated.

Bug: 187105270
Test: booted Cuttlefish twice, checked logs
Change-Id: I9c5c547140e8b1bbffb9c1d215f75251f0f1354e