Set logging level for requests via new Server options

[sushengloong]

Relating to gaqzi/gocd-cli#14, this PR will allow client to set logging level for requests via the new Server options using request_debug_level key which defaults to 0.
This should be helpful for debugging.

Sad to say my Python knowledge is very limited so I don't know how to unit test this. 😓
Any suggestion?

[henriquegemignani]

This appears to be fine on first look, but looking deeper request_debug_level is only used by _add_basic_auth and that is only used if you pass a user and password.

As for test, I'd say the important piece is that request_debug_level reaches urllib. So I suggest you mock the part of urllib that receives the debug level and then assert that it received the correct value.

[gaqzi]

@sushengloong this is the wrong place for this, since I know your use case, it should be handled in gocd-cli. Although adding this as an option and making it more available is a good idea!

The more pythonic way would be to have it as an argument with a default value, as the options = {} pattern can be handled completely with keyword arguments (which have been part of Python for a long time). :)