Reduce testsuite memory footprint

The testsuite uses a huge amount of memory as a consequence of some not-so-good patterns in the *TestCase classes.
The main issue is with static members of those classes being used to keep references to client proxies. While that is important to save cpu cycles, it ends up in a lot of "memory leaks" as once a testcase has been run, it's not needed/accessed anymore but still keep a hard link to the clients, preventing their garbage collection.