Packaging compability

Relax pip requirements so that more system packages may be used instead of pulling
 everything from pip

Add missing requirement to test-requirements: tox
Add pyOpenSSL to reqirements so available system packages can be used instead of
 haveing to recompile OpenSSL c bindings inside pip
`tox` is not needed here. It should be installed beforehand and use these requirements to build envs and it is not actually needed to run tests.