Removes support for Python 2.5

* Adds fallback to distutils if setuptools is not installed
* Removes the xmlrpc transport and moved the requests transport to SoftLayer/transport.py
* Adds make_rest_api_call to SoftLayer.transport and related tests. SoftLayer.metadata
  is currently the only thing that uses it. I think both of the transport types should have
  the same interface, but that's not the case at the moment.
* Removes requirement for simplejson if python version is less than 2.6.
* setup.py bails out early if the python version is less than 2.

This turned out to be a bigger change than I expected... Whoops. The metadata service needs to be verified on a CCI.