Fix PY3 compatibility

* Change iteritems to items
* Use six.string_types instead of basestring
* Use open instead of file
* encode to utf-8 before writing to file in tests
* fix minor relative import in mistralclient.utils

Also, this is blocking the port of Heat to use Python 3.

Change-Id: Ie82975482754246d9761dd2cf9693fb852024a9b

mistralclient/tests/unit/v2/test_cli_cron_triggers.py

@@ -41,7 +41,7 @@ class TestCLITriggersV2(base.BaseCommandTest):
     @mock.patch('mistralclient.api.v2.cron_triggers.CronTriggerManager.create')
     def test_create(self, mock, mock_open):
         mock.return_value = TRIGGER
-        mock_open.return_value = mock.MagicMock(spec=file)
+        mock_open.return_value = mock.MagicMock(spec=open)
 
         result = self.call(
             cron_triggers_cmd.Create,

mistralclient/tests/unit/v2/test_cli_environments.py

@@ -56,7 +56,7 @@ class TestCLIEnvironmentsV2(base.BaseCommandTest):
         mock.return_value = ENVIRONMENT
 
         with tempfile.NamedTemporaryFile() as f:
-            f.write(content)
+            f.write(content.encode('utf-8'))
             f.flush()
             file_path = os.path.abspath(f.name)
             result = self.call(environment_cmd.Create, app_args=[file_path])
@@ -74,7 +74,7 @@ class TestCLIEnvironmentsV2(base.BaseCommandTest):
         mock.return_value = ENVIRONMENT
 
         with tempfile.NamedTemporaryFile() as f:
-            f.write(content)
+            f.write(content.encode('utf-8'))
             f.flush()
             file_path = os.path.abspath(f.name)
             result = self.call(environment_cmd.Update, app_args=[file_path])

mistralclient/tests/unit/v2/test_cli_workbooks.py

@@ -53,7 +53,7 @@ class TestCLIWorkbooksV2(base.BaseCommandTest):
     @mock.patch('mistralclient.api.v2.workbooks.WorkbookManager.create')
     def test_create(self, mock, mock_open):
         mock.return_value = WORKBOOK
-        mock_open.return_value = mock.MagicMock(spec=file)
+        mock_open.return_value = mock.MagicMock(spec=open)
 
         result = self.call(workbook_cmd.Create, app_args=['wb.yaml'])
 
@@ -63,7 +63,7 @@ class TestCLIWorkbooksV2(base.BaseCommandTest):
     @mock.patch('mistralclient.api.v2.workbooks.WorkbookManager.update')
     def test_update(self, mock, mock_open):
         mock.return_value = WORKBOOK
-        mock_open.return_value = mock.MagicMock(spec=file)
+        mock_open.return_value = mock.MagicMock(spec=open)
 
         result = self.call(workbook_cmd.Update, app_args=['definition'])
 
@@ -113,7 +113,7 @@ class TestCLIWorkbooksV2(base.BaseCommandTest):
     @mock.patch('mistralclient.api.v2.workbooks.WorkbookManager.validate')
     def test_validate(self, mock, mock_open):
         mock.return_value = {'valid': True}
-        mock_open.return_value = mock.MagicMock(spec=file)
+        mock_open.return_value = mock.MagicMock(spec=open)
 
         result = self.call(workbook_cmd.Validate, app_args=['wb.yaml'])
 
@@ -124,7 +124,7 @@ class TestCLIWorkbooksV2(base.BaseCommandTest):
     @mock.patch('mistralclient.api.v2.workbooks.WorkbookManager.validate')
     def test_validate_failed(self, mock, mock_open):
         mock.return_value = {'valid': False, 'error': 'Invalid DSL...'}
-        mock_open.return_value = mock.MagicMock(spec=file)
+        mock_open.return_value = mock.MagicMock(spec=open)
 
         self.assertRaises(exc.MistralClientException,
                           self.call,

mistralclient/tests/unit/v2/test_cli_workflows.py

@@ -128,7 +128,7 @@ class TestCLIWorkflowsV2(base.BaseCommandTest):
     @mock.patch('mistralclient.api.v2.workflows.WorkflowManager.validate')
     def test_validate(self, mock, mock_open):
         mock.return_value = {'valid': True}
-        mock_open.return_value = mock.MagicMock(spec=file)
+        mock_open.return_value = mock.MagicMock(spec=open)
 
         result = self.call(workflow_cmd.Validate, app_args=['wf.yaml'])
 
@@ -139,7 +139,7 @@ class TestCLIWorkflowsV2(base.BaseCommandTest):
     @mock.patch('mistralclient.api.v2.workflows.WorkflowManager.validate')
     def test_validate_failed(self, mock, mock_open):
         mock.return_value = {'valid': False, 'error': 'Invalid DSL...'}
-        mock_open.return_value = mock.MagicMock(spec=file)
+        mock_open.return_value = mock.MagicMock(spec=open)
 
         self.assertRaises(exc.MistralClientException,
                           self.call,