tools/compile_and_test_for_board: assert resultdir is valid

Currently giving an absolute or outside of RIOT application breaks the
result directory evaluation which can lead to deleting the application.

Add an assertion to detect it.

dist/tools/compile_and_test_for_board/compile_and_test_for_board.py

@@ -232,6 +232,10 @@ class RIOTApplication():
         self.resultdir = os.path.join(resultdir, appdir)
         self.logger = logging.getLogger('%s.%s' % (board, appdir))
 
+        # Currently not handling absolute directories or outside of RIOT
+        assert is_in_directory(self.resultdir, resultdir), \
+            "Application result directory is outside main result directory"
+
     # Extract values from make
     def name(self):
         """Get application name."""