Disable Httplib2 server authorization type requests for each Prestashop API request.

Added additional flag ```auth_type``` in the ```Http``` class of the Httplib2 library and call ```set_auth_type("basic")``` in the Prestapyt library if the Httplib2 has the method ```set_auth_type```.
This flag sets server authorization type and disables automatic detection for each request because I send 50000 requests and I don't need authorization type detection requests in the same amount. Each request has unique URI - this is the REST API requests. Therefore I set server authorization type directly with the call ```self.http_client.set_auth_type("basic")```.
Httplib2 pull request: https://github.com/uggedal/httplib2/pull/1