Fix test_rule.py error

[nsano-rururu]

elasticsearch-py	Test Run	Send real alerts
7.0.0	〇	〇
7.10.0	✖	✖
7.10.0	〇 (fix test_rules.py )	✖
7.10.0	〇 (fix test_rules.py )	〇 (Fix initializing self.thread_data.alerts_sent for running elastalert-test-rule #2991)

[jertel]

Confirmed that the PR improves the usage of the ES API based on the ES 7.10 documentation located here: https://elasticsearch-py.readthedocs.io/en/v7.10.1/api.html#elasticsearch

[nsano-rururu]

I've seen the following warning when running ElastAlertServer on Elasticsearch-py 7.10.0: It seems that the new version of Elasticsearch-py now warns you of what will be deprecated in the next major version.

I'm a co-maintainer of https://github.com/johnsusek/praeco and https://github.com/johnsusek/elastalert-serverr, so I installed it in ElastAlert Server in my local environment and tested it.

16:13:49.571Z ERROR elastalert-server:
    ProcessController:  /home/node/.local/lib/python3.8/site-packages/elasticsearch/connection/base.py:190: ElasticsearchDeprecationWarning: Camel case format name dateOptionalTime is deprecated and will be removed in a future version. Use snake case name date_optional_time instead.
      warnings.warn(message, category=ElasticsearchDeprecationWarning)
    /home/node/.local/lib/python3.8/site-packages/elasticsearch/connection/base.py:190: ElasticsearchDeprecationWarning: [types removal] Using include_type_name in put mapping requests is deprecated. The parameter will be removed in the next major version.
      warnings.warn(message, category=ElasticsearchDeprecationWarning)