Unittest - Add mechanism to skip task and taskd tests

* When testing multiple clients vs server versions, repeating client
tests is unnecessary. By setting the env variables TASKW_SKIP and
TASKD_SKIP it will now be possible to skip all task (client only) and
taskd (client + server) tests, respectively.

test/basetest/__init__.py

@@ -2,6 +2,6 @@
 
 from .task import Task
 from .taskd import Taskd
-from .testing import TestCase
+from .testing import TestCase, ServerTestCase
 
 # vim: ai sts=4 et sw=4