Test Elasticsearch queries

[Lorygold]

Add the tests for the Elasticsearch queries, so for the tasks.exec_process_logs and tasks.process_user functions.

Test also with some logs where the user.name and/or the source.ip fields don't exist (the .query("exists", field="[...]") filter should exclude them.

REMEMBER: After the tests you have to tearDown the Elastic data with:

def tearDown(self):
        ElasticQuery.objects.all().delete()