Automated tests for updater app

[PVince81]

Don't only automatically test 9.0.2->9.0.3 (the latest version) but also from previous versions to 9.0.3.

Could help avoid discovering issues like owncloud/updater#358 too later.

[PVince81]

@jvillafanez do we have such tests ? Do they check integrity at the end ?

[jvillafanez]

Nope. I don't think we have any automatic tests with the updater app. The tests we have are for the occ upgrade command; these ones include the integrity check at the beginning and at the end of the upgrade process

[PVince81]

Some ideas: write behat tests similar to the ones we have in core but which are independent from the install. This idea could build up on top of this other idea: #329

So if the test is able to setup a tarball, it can also use OCC commands to change config.php's link to a test update server (if needed). And for the "lastupdatedat" refresh the value can be deleted using the "occ config:*" commands.

Not sure if behat would be overkill in this case. We might want to add additional assertion cases to check after the update and also some preconditions (ex: LDAP was setup + some users + encryption) before running the update.

[PVince81]

cc @davitol