In-process swift server for functional tests

This patch changes the behavior of the functional tests such that when
both /etc/swift/swift.conf and /etc/swift/test.conf are _not_ present
on the system where the functional tests are executed, an in-process
functioning swift environement will be established, akin to the one
used in test/unit/proxy/test_server.py, and all the functional tests
will be executed against it.

This then allows one to use the coverage options to see how well
functional tests exercise code paths, or more easily debug existing
functional tests or write new ones.

Change-Id: I5acd65e3068868d6509feae1d1954237d37fad45