Constantly reload Kubernetes config

[adamnovak]

This (written on top of #2868) will fix #2867 by reloading the Kubernetes config and making a new API clients every 5 minutes, as suggested in kubernetes-client/python#741 (comment).

We'll still get in trouble if we have a single watch or loop over pods that runs for more than the credential expiration time, but that seems unlikely to happen and would be its own slowness problem anyway.

[adamnovak]

@DailyDreaming I got what I think is an unrelated test failure from the Python 2 integration tests:

_ EncryptedAWSJobStoreTest.test_testImportSharedFile__otherCls_awsjobstoretest _
Traceback (most recent call last):
  File "/builds/databiosphere/toil/src/toil/test/jobStores/jobStoreTest.py", line 1061, in setUp
    super(AbstractEncryptedJobStoreTest.Test, self).setUp()
  File "/builds/databiosphere/toil/src/toil/test/jobStores/jobStoreTest.py", line 124, in setUp
    self.jobstore_initialized.initialize(self.config)
  File "/builds/databiosphere/toil/src/toil/jobStores/aws/jobStore.py", line 148, in initialize
    super(AWSJobStore, self).initialize(config)
  File "/builds/databiosphere/toil/src/toil/jobStores/abstractJobStore.py", line 146, in initialize
    self.writeConfig()
  File "/builds/databiosphere/toil/src/toil/jobStores/abstractJobStore.py", line 154, in writeConfig
    pickle.dump(self.__config, fileHandle, pickle.HIGHEST_PROTOCOL)
  File "/usr/lib/python2.7/contextlib.py", line 24, in __exit__
    self.gen.next()
  File "/builds/databiosphere/toil/src/toil/jobStores/aws/jobStore.py", line 552, in writeSharedFileStream
    yield writable
  File "/usr/lib/python2.7/contextlib.py", line 24, in __exit__
    self.gen.next()
  File "/builds/databiosphere/toil/src/toil/jobStores/aws/jobStore.py", line 1122, in uploadStream
    assert bool(self.version) == (self.content is None)
AssertionError

I'm going to rerun the test, but we also might have a bug.

[DailyDreaming]

LGTM.