Export default location of password file

tripleo-client stores generated passwords into a
file in a default location.

Other modules might need to know this location
(e.g. tripleo-passwords-rotate [1]), so expose
this default value in tripleo-common.

[1] I69361215efcca69c1bbeb24f427a0c309ff2806f

Related-Bug: #1960527
Change-Id: Ib799533e2a60413620639bc9d0af44ac31006159

tripleo_common/constants.py

@@ -13,6 +13,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import os
 
 #: The resource name used for package updates
 UPDATE_RESOURCE_NAME = 'UpdateDeployment'
@@ -180,3 +181,11 @@ INVENTORY_NETWORK_CONFIG_FILE = 'inventory-network-config.yaml'
 # Hard coded name in:
 #   tripleo_ansible/ansible_plugins/modules/tripleo_ovn_mac_addresses.py
 OVN_MAC_ADDR_NET_NAME = 'ovn_mac_addr_net'
+
+# Default directory for the overcloud deployment, where all inputs,
+# outputs and generated files are stored
+DEFAULT_WORKING_DIR_FORMAT = os.path.join(os.environ.get('HOME', '~/'),
+                                          'overcloud-deploy', '{}')
+
+# Format for password filename
+PASSWORDS_ENV_FORMAT = '{}-passwords.yaml'