Update cred provider to have more general date parser

Also, the default time fetcher now returns time zone aware
local time.  This results in no external function change,
but it does allow for more generalized date string formats
to be provided (it uses dateutil.parser.parse() to parse
timestamps now).
Cleanup test_credentials formatting

* pep8
* remove unused imports
* remove unused vars
* adding missing assertion to a test
Merge branch 'tz-aware-cred-refresh' into develop

* tz-aware-cred-refresh:
  Cleanup test_credentials formatting
  Update cred provider to have more general date parser