Add Steps to perform HTTP requests
Formating of the doc
Modification after review comments
port HTTPStep to txrequests

This makes this step asynchronous and suitable for buildbot

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>
http step cleanup and test

- add GPL header
- change coding style
- add tests

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>
Merge branch 'txrequests' of git://github.com/tardyp/buildbot