[TRAIN] Default ceph export config-download dir to mistral

When [1] was backported it should have used the defaults
that train has which were removed by the work on bug
1874432. This patch is going directly into Train only so
that Train users may have a better default.

[1] https://review.opendev.org/754402

Change-Id: I943723a04d2a8cc1bb46ba0c55d395410c14486c
Closes-Bug: #1905471

tripleoclient/tests/v1/test_overcloud_export_ceph.py

@@ -11,8 +11,6 @@
 #   WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #   License for the specific language governing permissions and limitations
 #   under the License.
-import os
-
 import mock
 
 from osc_lib.tests import utils
@@ -61,6 +59,6 @@ class TestOvercloudExportCeph(utils.TestCommand):
 
         with mock.patch('six.moves.builtins.open', self.mock_open):
             self.cmd.take_action(parsed_args)
-        path = os.path.join(os.environ.get('HOME'), 'config-download')
+        path = '/var/lib/mistral'
         mock_export_ceph.assert_called_once_with('dcn0', 'openstack', path)
         self.assertEqual(data, mock_safe_dump.call_args[0][0])

tripleoclient/v1/overcloud_export_ceph.py

@@ -66,7 +66,7 @@ class ExportOvercloudCeph(command.Command):
                             action='store',
                             help=_('Directory to search for config-download '
                                    'export data. Defaults to '
-                                   '$HOME/config-download'))
+                                   '/var/lib/mistral'))
 
         return parser
 
@@ -91,8 +91,7 @@ class ExportOvercloudCeph(command.Command):
                 "File '%s' already exists, not exporting." % output_file)
 
         if not parsed_args.config_download_dir:
-            config_download_dir = os.path.join(os.environ.get('HOME'),
-                                               'config-download')
+            config_download_dir = '/var/lib/mistral'
         else:
             config_download_dir = parsed_args.config_download_dir