Bug 1096920 - Add test to delete entire call log when it has several cal...

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Robert, that's all right. I tried myself yesterday too, I couldn't get it working either.
It's strange, because I really think this should be working. It might be a good idea to file a bug on this, to find out what's going on here.

As an alternative, you could perhaps use a Wait for condition
And then use:  self.marionette.execute_async_script('window.wrappedJSObject.CallLogDBManager.getRecentList(function(recents) {marionetteScriptFinished(recents.length);})')
This should return 2 after those 2 CallLogDBManager.add calls, but for some reason, it stays 1.

But I guess this should be tackled in a follow-up bug to get rid of this time.sleep(1) call.
You might want to file this bug already and then mention the bug number as a comment before the time.sleep(1) call.

I don't really have any more review comments at this point. 
I'll review your patch once again, you've addressed review comments from @jlorenzo.