Add possibility to create Failure from exception

In some cases it's great to have possibility to create
misc.Failure object from an exception directly. This
commit adds the 'from_exception' class method to create
misc.Failure in such way.

Change-Id: I44ae6720196b7bbe1e4ad538018487f0761a1af5

taskflow/tests/unit/test_utils_failure.py

@@ -99,6 +99,13 @@ class ReCreatedFailureTestCase(test.TestCase, GeneralFailureObjTestsMixin):
         self.assertIs(exc.check(RuntimeError), RuntimeError)
 
 
+class FromExceptionTestCase(test.TestCase, GeneralFailureObjTestsMixin):
+
+    def setUp(self):
+        super(FromExceptionTestCase, self).setUp()
+        self.fail_obj = misc.Failure.from_exception(RuntimeError('Woot!'))
+
+
 class FailureObjectTestCase(test.TestCase):
 
     def test_dont_catch_base_exception(self):

taskflow/utils/misc.py

@@ -416,6 +416,10 @@ class Failure(object):
                     'Failure.__init__ got unexpected keyword argument(s): %s'
                     % ', '.join(six.iterkeys(kwargs)))
 
+    @classmethod
+    def from_exception(cls, exception):
+        return cls((type(exception), exception, None))
+
     def _matches(self, other):
         if self is other:
             return True