Fixes action result serialization

Attempt to serialize value that contained array of strings caused
endless recursion.

Change-Id: I5fe5b30b6d7ad6521a00ac3cbad21dccd812791d
Closes-Bug: #1435437

murano/dsl/serializer.py

@@ -26,7 +26,8 @@ class ObjRef(object):
 
 
 def serialize_object(obj):
-    if isinstance(obj, (collections.Sequence, collections.Set)):
+    if isinstance(obj, (collections.Sequence, collections.Set)) and not \
+            isinstance(obj, types.StringTypes):
         return [serialize_object(t) for t in obj]
     elif isinstance(obj, collections.Mapping):
         result = {}

murano/tests/unit/dsl/meta/SampleClass2.yaml

@@ -4,3 +4,15 @@ Properties:
   class2Property:
     Contract: $.string().notNull()
 
+Methods:
+  testMethod:
+    Body:
+      Return:
+        key1: abc
+        key2: [a, b, c]
+        key3: null
+        key4: false
+        key5:
+          x: y
+        key6:
+          - w: q

murano/tests/unit/dsl/test_results_serializer.py

@@ -17,6 +17,7 @@ import types
 
 from testtools import matchers
 
+from murano.dsl import serializer
 from murano.tests.unit.dsl.foundation import object_model as om
 from murano.tests.unit.dsl.foundation import test_case
 
@@ -123,3 +124,21 @@ class TestResultsSerializer(test_case.DslTestCase):
         self.assertEqual(
             'John Snow',
             runner2.on(self._class1).testAttributes('John'))
+
+    def test_value_deserialization(self):
+        """Test serialization of arbitrary values that can be returned
+        from action methods
+        """
+
+        runner = self.new_runner(self._class2)
+        result = runner.testMethod()
+        self.assertEqual(
+            {
+                'key1': 'abc',
+                'key2': ['a', 'b', 'c'],
+                'key3': None,
+                'key4': False,
+                'key5': {'x': 'y'},
+                'key6': [{'w': 'q'}]
+            },
+            serializer.serialize_object(result))