test_app_server: Fix the build.

It doesn't work, however; it throws an error message about failing to connect
to a port, which I presume was caused by the launch_daemon changes. If
Axel could take a look at it, that'd be much appreciated...

app_server: fix test-app_server for launch_daemon changes

* Make test-app_server work again in a launch_daemon environment

* test_registrar gets a separate signature and port name again so the
host system can distinguish it from the system registrar

* AppServer is normally a BServer now, however, there can't be two
BApplications in one team. A class TestServerLoopAdapter is added,
which becomes the base class of AppServer instead of BServer when
compiling for libbe_test. It's an adapter class which looks towards
AppServer as it if was a BServer, but internally it is derived from
MessageLooper (like the old AppServer before the transition to
BServer).

This way, AppServer can stay a BServer in normal builds and it also
avoids having to use too many #ifdefs to distinguish the two
versions.