Allow running server-only tests

[Aaron1011]

It's not always necessary to spawn a full client. McTester should allow specifying the platform that a test should be run on.

There are two ways of handling a mix of server-only and client tests:

1. Start both the client and server on JUnit startup. This decreases execution time, but dramatically increases memory usage, since both a sever and client are running at the same time.
2. Run all of the tests for one platform, stop the server (or client), then start the platform for the other tests. This decreases peak memory usage, but will probably add anywhere from 30-60 seconds to overall execution time.

There could be a JVM argument to toggle between these modes, since they shouldn't have any impact on test results.