proxy: mirror structure of marconi queues + bootstrap

This patch adds smarter configuration to the proxy in two steps:

1. mirror the transport implementation used in marconi.queues in
   marconi.proxy
2. add a bootstrap file to take care of start up

Rationale: make configuration work, make deploying easy, make
alternate transport implementations feasible.

Another change: the unit tests are fixed by adding a few changes:
1. add drop functionality to the proxy storage interface
2. use drop/flush in test suite tearDown
3. rm tests.unit.test_config
4. delete queues at the end of the catalogue test (not yet robust)

The rationale for (3) was that test_config did not play nice with
other tests when they were registering their options, and failed as a
result. Furthermore, we should not need to test oslo.config.

Configuration changes: new fields in etc/marconi.conf
- drivers:proxy
- drivers:proxy:storage:{memory.mongodb}
- drivers:proxy:transport:wsgi
- oslo_cache

Also, fix: InternalServerError -> HTTPInternalServerError

Finally, redis was removed from requirements.txt.

Change-Id: If2365a1a738a3975fe6bde7bd07dfdee3460cecd
Implements: blueprint placement-service
Merge "proxy: mirror structure of marconi queues + bootstrap"