Make get_all_server_info and get_scaling_group_servers use pure-http

The metrics.py code had to be updated to deal with this, and I refactored the effectiness a little bit into metrics.py, so that there's a new get_all_metrics_effects function extracted from get_all_metrics.

I've added unit tests for get_all_metrics_effects, and left the unit tests for get_all_metrics in place (and updated them to ensure that code is using pure-HTTP properly). The tests for that are pretty nasty, but hopefully they'll go away if more of metrics.py gets Effect-ified.


I wonder if this can be Nova-bound request function. I wrote `get_load_balancer_contents` assuming it gets CLB-bound request function. Not sure if its a good idea.