Fix SimpleReadOnlyNovaManageTest.test_flavor_list CLI test

'nova-manage flavor list' should equal 'nova-manage instance_type list'

Adds an option, merge_stderr, that when enabled redirects stderr to
stdout.

Fix bug 1159914

Change-Id: Icfb93f3fd1f1d6f14a73b4873a6dad36122d3a98
diff --git a/cli/simple_read_only/test_compute_manage.py b/cli/simple_read_only/test_compute_manage.py
index 5768c74..0fa84bd 100644
--- a/cli/simple_read_only/test_compute_manage.py
+++ b/cli/simple_read_only/test_compute_manage.py
@@ -50,6 +50,7 @@
         self.nova_manage('', '-h')
 
     def test_version_flag(self):
+        # Bug 1159957: nova-manage --version writes to stderr
         self.assertNotEqual("", self.nova_manage('', '--version'))
         self.assertEqual(self.nova_manage('version'),
                          self.nova_manage('', '--version'))
@@ -68,8 +69,9 @@
 
     def test_flavor_list(self):
         self.assertNotEqual("", self.nova_manage('flavor list'))
-        self.assertNotEqual(self.nova_manage('instance_type list'),
-                            self.nova_manage('flavor list'))
+        self.assertEqual(self.nova_manage('instance_type list',
+                                          merge_stderr=False),
+                         self.nova_manage('flavor list', merge_stderr=False))
 
     def test_db_archive_deleted_rows(self):
         # make sure command doesn't error out