Elasticsearch `get_load` throws warning trying to return JSON

This issue has shown up in a previous issue in the repo, but it appears that sometime along the line the elasticsearch Python API changed to return dictionaries instead of the current behavior which is to return a dictionary of the job cache.

Originally posted by @msteed in https://github.com/saltstack/salt/issues/23125#issuecomment-140512958

$ salt --versions-report
Salt Version:
           Salt: 2019.2.0

Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: 2.4.2
      docker-py: Not Installed
          gitdb: 0.6.4
      gitpython: 1.0.1
          ioflo: Not Installed
         Jinja2: 2.8
        libgit2: Not Installed
        libnacl: Not Installed
       M2Crypto: Not Installed
           Mako: 1.0.3
   msgpack-pure: Not Installed
 msgpack-python: 0.4.6
   mysql-python: Not Installed
      pycparser: Not Installed
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: Not Installed
         Python: 2.7.12 (default, Nov 12 2018, 14:36:49)
   python-gnupg: 0.3.8
         PyYAML: 3.11
          PyZMQ: 15.2.0
           RAET: Not Installed
          smmap: 0.9.0
        timelib: Not Installed
        Tornado: 4.2.1
            ZMQ: 4.1.4

System Versions:
           dist: Ubuntu 16.04 xenial
         locale: UTF-8
        machine: x86_64
        release: 4.4.0-148-generic
         system: Linux
        version: Ubuntu 16.04 xenial

$ pip freeze | grep elastic
elasticsearch==6.4.0

$ salt salt elasticsearch.info
salt:
    ----------
    cluster_name:
        elasticsearch_calvin
    cluster_uuid:
        GjYi_ICTQJGolj3Lo42DQg
    name:
        Yv7_FY8
    tagline:
        You Know, for Search
    version:
        ----------
        build_date:
            2019-05-15T20:06:13.172855Z
        build_flavor:
            oss
        build_hash:
            65b6179
        build_snapshot:
            False
        build_type:
            tar
        lucene_version:
            7.7.0
        minimum_index_compatibility_version:
            5.0.0
        minimum_wire_compatibility_version:
            5.6.0
        number:
            6.8.0

Start at the Salt Elasticsearch integration entry point for get_load and reproduce the warning with elasticsearch 6.4.0, comparing its response shape with the current handling. Confirm the expected dictionary result and verify that the command returns JSON without the warning across the relevant Elasticsearch API behavior.