Recover from missing upgrade to system package.

When a system app has been upgraded, we mark the built-in version as
disabled, and skip it when parsing built-in apps, since we expect
the userdata version to be scanned a few moments later.

However, in very rare cases we can end up missing the expected
userdata version, and we'd end up dropping the package entirely, even
though we have a built-in version to fall back to.  This change
handles that case by rescanning and enabling the built-in version when
the userdata version never materializes.

Also include critical log messages in check-in dumpsys to help track
down how we ended up in this state.

Bug: 17805839
Change-Id: I9971f882f9bb8ab7934c20b04e0b72366c4d04d0