Make sure cli CommandFailed prints out stdout and stderr

Having a CommandFailed exception without stdout is very confusing, lets
fix that.

subprocess.CalledProcessError doesn't print out stderr or stdout so use
our own error that does.

Change-Id: I3bf75d6f526bdc58e64bbc7d83911e9d63e4b801

test_command_failed.py

@@ -0,0 +1,30 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from tempest import cli
+from tempest.tests import base
+
+
+class TestOutputParser(base.TestCase):
+
+    def test_command_failed_exception(self):
+        returncode = 1
+        cmd = "foo"
+        stdout = "output"
+        stderr = "error"
+        try:
+            raise cli.CommandFailed(returncode, cmd, stdout, stderr)
+        except cli.CommandFailed as e:
+            self.assertIn(str(returncode), str(e))
+            self.assertIn(cmd, str(e))
+            self.assertIn(stdout, str(e))
+            self.assertIn(stderr, str(e))