wait_for_log looks at crio logs and waits for the given message to appear.
If the message is already in the logs, it gets out immediately.

To allow waiting for another occurence of the same message, we're making
it output the timestamp of the first occurence that it finds.
The caller can keep that information and provide it as a second parameter
to wait_for_log, in which case wait_for_log will start waiting for
the message after the given timestamp.

Signed-off-by: Julien Ropé <jrope@redhat.com>

As the test is doing multiple reloads, it was hard to use wait_for_log to synchronize
on the end of the reload process.
With the modification on wait_for_log to allow waiting for multiple occurences of a
log message, we can simplify this test, and make sure it's actually in sync.

Keeping only one "wait_for_log" calls should be enough then - no need for multiple
synchronization points, and the config validation is done by the calls to "crictl images".

Fixes: cri-o#8324

Signed-off-by: Julien Ropé <jrope@redhat.com>