Fix log checking in PRH so that only entries generated during test execution are...

Fix log checking in PRH so that only entries generated during test execution are taken into account.

- fixing "Should not send PNF ready when DMaaP event is not JSON array" test that was passing due to checking log entry generated by a previous test
- improving logs generated by keyword waiting for log entry
- changing 'find log entry' to 'wait for log entry' with explicit timeout setting
- adjusting timeouts for waiting for log entries to appear (20s is enough when prh workflow execution is scheduled every 10s)

Change-Id: I20c67dfce6e8d1809d24ddb3108a088b00165996
Issue-ID: DCAEGEN2-1544
Signed-off-by: grabinsk <maciej.grabinski@nokia.com>