LIBCLOUD-288 - Do xmlrpc requests using the libcloud http layer

2nd part of my XML-RPC efforts. It pulls the shared code out of my Gandi proof of concept and updates VCL and SoftLayer to use it as well.

Tests are passing, my Gandi manual tests are working, i've pep8'd all the files i've touched.

The PR contains my earlier Gandi PR as it hasn't landed in trunk yet, but I can easily rebase this patch if the earlier patch lands.