Multiple fixes for PEP8 and unittests

Fix multiple PEP8-related issues.
Fix unittests for config schema registry.
Delete broken joker unittests.
Ignore F401,F403,E501,H306 in flake8 section of tox.ini:
  * allow non-alphabetical ordering of imports
  * ignore line length limit of 80
  * allow wildcard imports
  * allow importing unused modules for future use

Change-Id: Iac1bb030900c009e39a73fb98b5d76c24372920d