In-process swift server for functional tests

Provide a way to run the functional tests using a p/a/c/o server setup
in the same process.

By setting the environment variable, SWIFT_TEST_IN_PROCESS, the
functional test set up will construct a proxy, account, container and
object server running in the same process as is running the functional
tests, ignoring any external swift service.

This patch also 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 executing, 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.

Previously, if no /etc/swift/swift.conf and /etc/swift/test.conf files
were found, the tests would just be marked as skipped.

Using this in-process method allows one to gather code coverage using
the functional tests to exercise code paths, in addition to the unit
tests, or more easily debug existing functional tests or write new
ones.

Change-Id: I5acd65e3068868d6509feae1d1954237d37fad45