Fix address in use bug in tests

Added a delay before starting the new server, only starting server once
in ServiceClientTest as it was not required to shutdown each time.
Shutting down let to complete thread termination so that other tests
would not be executed anymore.

Change-Id: I81f538669a8634e4b9add95fda7783fd5b63e72a
Signed-off-by: Denis Knoepfle <denis.knoepfle@sap.com>