Testing SoftLayer.CLI.main()

Makes SoftLayer.CLI.main() testable so we can start making Unit/functional tests with the CLI code directly.

I added an env class that should includes all that's needed to find/load/execute plugins. By mocking the functionality, we can write tests that fully tests the CLI aspect of the library.

This relies on the housekeeping work done earlier so it depends on #29. The extra commits will show in this pull request until #29 is merged in.