Cluster creation fails on discovery when behind a proxy even after providing proxy information

[Stephen Watson]

When Magnum creates a cluster from behind a proxy the command will fail inside magnum.drivers.template_def during discovery and discovery address validation (get_discovery_url() and validate_discovery_url(), respectively).

The calls fail to provide any proxy information to the requests package on making the command, regardless of whether that information has been set in the http_proxy or https_proxy command parameters.