Make endpoint type configurable

Rally is supposed to honor endpoint_type being defined as part of a
deployment configuration, which is currently broken. This patch
works around it by replacing all the hard coded passing of "public"
to make it a config option.

Change-Id: I759fc1bdff4e0e71ea4cb5576612d713fe84eb35
Disassociate Nova networks during cleanup

Closes-bug: #1350517

Add a dirty hack to deal with cleaning up associated Nova networks
after a Rally run. This was originally being done via the cleanup
classes but after discussing with Boris, it was determined this was
the least-bad way to approach the problem.

Change-Id: Ic52bb0d156dc2adebc9bca2daec660f81d16b31c