feat: separate config for queues and proxy

This patchset separates the configuration of the proxy from that of
the queues server. This was done in order to simplify the
configuration file for each, and because it is not expected that the
proxy and the queues servers would be launched on the same
host. Furthermore, many of the proxy options are not relevant to the
queues server.

Furthermore, to allow this, common.config had to be modified to take a
prog parameter. This enabled the ability to save multiple
configuration files to one directory. See below for details.

The new files are:
- etc/marconi-proxy.conf
- etc/marconi-queues.conf

They are expected to be saved to one of:
- ~/.marconi
- /etc/marconi

Regarding namespaces, queues specific options are associated with the
'queues:*' group and proxy specific options are associated to the
'proxy:*' group.

The appropriate changes are also applied to the test suite and
helpers.

Change-Id: I7cf25e47ecff47934b50c21000b31308e1a4c8a9
Implements: blueprint placement-service
Merge "feat: separate config for queues and proxy"