Use the real `logging` module.

It will still be a NOOP operation since the module is already loaded.
`salt.log` is now a package instead of a module.

The necessary changes were made to assure backwards compatibility.
Added a `salt.log.handlers` module which includes a queue handler.

We now use a queue handler instead of a null handler in order to show **all** log message records, at a latter stage, when we can, finally, show log messages.
Use proper pip mirrors in `integration.states.virtualenv.VirtualenvTest.test_issue_2594_non_invalidated_cache`