Executes all linters via pre-commit, which is much faster, guarantees
their version locking and allows upgrading them with a single command.
Before this change the only linter running via pre-commit was
ansible-lint.
Now we also run bashate, flake8 and yamllint via pre-commit.
For developer convenience we still keep the old tox environments
which allow running a single linter.
Added long_description_content_type to fix twine check failure
Change-Id: I037eae61921b2a84aa99838804f70e96ee8d8b13
b541c5ef99