Fix type error

[celenechang]

What does this PR do?

Fixes a pickle error introduced for py2 in #5447

kubernetes_state (5.2.0)
    ------------------------
      Instance ID: kubernetes_state:d52437eab9dd94d4 [ERROR]
      Configuration Source: file:/etc/datadog-agent/conf.d/kubernetes_state.d/auto_conf.yaml
      Total Runs: 95
      Metric Samples: Last Run: 0, Total: 0
      Events: Last Run: 0, Total: 0
      Service Checks: Last Run: 0, Total: 0
      Average Execution Time : 0s
      Last Execution Date : 2020-02-26 18:59:57.000000 UTC
      Last Successful Execution Date : Never
      Error: can't pickle dictionary-keyiterator objects
      Traceback (most recent call last):
        File "/opt/datadog-agent/embedded/lib/python2.7/site-packages/datadog_checks/base/checks/base.py", line 693, in run
          instance = copy.deepcopy(self.instances[0])
        File "/opt/datadog-agent/embedded/lib/python2.7/copy.py", line 163, in deepcopy
          y = copier(x, memo)
        File "/opt/datadog-agent/embedded/lib/python2.7/copy.py", line 257, in _deepcopy_dict
          y[deepcopy(key, memo)] = deepcopy(value, memo)
        File "/opt/datadog-agent/embedded/lib/python2.7/copy.py", line 163, in deepcopy
          y = copier(x, memo)
        File "/opt/datadog-agent/embedded/lib/python2.7/copy.py", line 230, in _deepcopy_list
          y.append(deepcopy(a, memo))
        File "/opt/datadog-agent/embedded/lib/python2.7/copy.py", line 182, in deepcopy
          rv = reductor(2)
      TypeError: can't pickle dictionary-keyiterator objects

observed from the output of agent status

Motivation

Additional Notes

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
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