In my particular case I need to use a separate HTTP proxy to access my
OpenStack API than what is set in the environment. This commit adds an
optional parameter to the builder configuration and overrides the
net/http client that is used by the gophercloud library.
This change adds base support for an openstack builder.
Thank you to Rackspace for providing cloud assets to complete this work
and @sam-falvo for working with us on the perigee/gophercloud changes.