Acceptance tests: refactor wait_for_console_pattern

Acceptance tests: refactor wait_for_console_pattern

The same utility method is already present in two different test
files, so let's consolidate it into a single utility function.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Message-Id: <20190916164011.7653-1-crosa@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
[PMD: failure_message is optional]
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Message-Id: <20191028073441.6448-3-philmd@redhat.com>
Signed-off-by: Cleber Rosa <crosa@redhat.com>