Allow APK rollback without rollback capability on previous key

Currently if an APK rollback is requested after an update to an APK
that just rotated its signing key the rollback will only be allowed
if the previous signing key in the lineage has the rollback
capability granted. This commit allows a rollback to the previously
installed APK without requiring the rollback capability if the
rollback API is used. This allows apps to take advantage of APK
rollbacks without losing the benefit of key rotation by needing to
set the rollback capability on the previous signing key.

Bug: 175231724
Test: atest RollbackTest
Test: atest RollbackManaagerTest
Test: atest PkgInstallSignatureVerificationTest
Change-Id: I460ef4e7d4c221509b6442f2e8d3079229ad07c8