[Refactoring] Remove static members in WorkspaceDriver and provide a @TestRule

[hchauvin]

I think that in terms of ergonomics:

1. The static members in WorkspaceDriver should be moved to an Environment class that would be shared to different instances of WorkspaceDriver (through a constructor, e.g. WorkspaceDriver(Environment environment, String bazelVersion)).

2. A default, shared Environment should be provided by a TestRule implementation of WorkspaceDriver (WorkspaceDriverTestRule) which would set up everything for a JUnit test. I do not advocate here for putting the Environment in a ClassRule, I was more thinking about a singleton.

3. BazelBaseTestCase should be removed.