tree 75bf0c4d1a5d208778956384a6616281b30b2dfc
parent 52d942c13a8bcf2b2a39498469c6b73dcb3da456
author Patrick Hiesel <hiesel@google.com> 1584539071 +0100
committer Patrick Hiesel <hiesel@google.com> 1584545270 +0100

Allow for an online migration of checker ref

This commit is a follow-up to the checker ref migration. It allows
for an online migration, that is, a migration while the system is
running. To do so, we check if the legacy ref exists and use it,
if it does.
This way, we can roll out the new code without having to migrate
the refs in the same go. It also allows for rollbacks more easily.

The code will use the new ref, if the legacy ref does not exist.

We add a test to assert the behavior and apply some finishing
touches to the existing test code was well as move the migration
class from the 'api' to the 'db' package.

Change-Id: I86dea2bd1617cf0ec0db35b6cee59630e9e136a4