small fixes for testing bugs

[LeXofLeviafan]

fixes #666:

• removing URL queries from testcase IDs for test_network_handler_with_url (thus shortening cassette names)

fixes #667:

• removing dependency on external binary for pylint validation

also:

• removing a no-longer-default check from pylint disable list to get rid of the warning
• adding a venv/ folder to linter exceptions to allow for convenient virtualenv placement
• updating flask-reverse-proxy-fix version in bukuserver/requirements.txt to match setup.py

P.S. Is it actually necessary for .pylintrc to be placed in tests/? It's used globally, so it would make more sense to just move it into the repo root and not have to specify a path. It would also allow to move path exceptions into the config file.

[jarun]

Thank you!