add group decorator and smoke test group

The smoke group is intended to be very fast while covering most important
features.
diff --git a/src/python/oftest/testutils.py b/src/python/oftest/testutils.py
index fef34f4..fe53ecc 100644
--- a/src/python/oftest/testutils.py
+++ b/src/python/oftest/testutils.py
@@ -1044,3 +1044,14 @@
     """
     cls._disabled = True
     return cls
+
+def group(name):
+    """
+    Testcase decorator that adds the test to a group.
+    """
+    def fn(cls):
+        if not hasattr(cls, "_groups"):
+            cls._groups = []
+        cls._groups.append(name)
+        return cls
+    return fn