Remove http_handler config option in auth_token

This option was predominately used so that we could substitute a fake
handler in place so that we could mock our HTTP calls. This has been
replaced for some time now with httpretty so is no longer necessary.

Change-Id: I8613f4e189ee977f17b9606547840d5e7847d77a
Merge "Remove http_handler config option in auth_token"