Split up reframe tests and pytest unit tests

reframe_tests/utilities/deferrable.py

@@ -0,0 +1,9 @@
+import os
+
+import reframe.utility.sanity as sn
+
+
+@sn.deferrable
+def path_join(*path):
+    """Deferable version of os.path.join"""
+    return os.path.join(*path)