Unify error messages

Unify error messages for CLI

Unify error messages for hub

Fixes: https://pagure.io/koji/issue/2720

tests/test_cli/test_list_hosts.py

@@ -0,0 +1,28 @@
+from __future__ import absolute_import
+
+import mock
+from six.moves import StringIO
+
+import koji
+from koji_cli.commands import anon_handle_list_hosts
+from . import utils
+
+
+class TestListHosts(utils.CliTestCase):
+    def setUp(self):
+        self.options = mock.MagicMock()
+        self.options.debug = False
+        self.session = mock.MagicMock()
+        self.session.getAPIVersion.return_value = koji.API_VERSION
+
+    @mock.patch('sys.stderr', new_callable=StringIO)
+    def test_list_pkgs_non_exist_channel(self, stderr):
+        channel = 'test-channel'
+        expected = "Usage: %s list-hosts [options]\n" \
+                   "(Specify the --help global option for a list of other help options)\n\n" \
+                   "%s: error: No such channel: %s\n" % (self.progname, self.progname, channel)
+        self.session.getChannel.return_value = None
+        with self.assertRaises(SystemExit) as ex:
+            anon_handle_list_hosts(self.options, self.session, ['--channel', channel])
+        self.assertExitCode(ex, 2)
+        self.assert_console_message(stderr, expected)