Search for vault credetials file.

During testing the vault credentials are stored on the lead unit.
Unfortunatly which unit is the designated leader can change during
the life of the test (particularly if the test involves rebooting
vault units). This change adds a function to search the units for
the credentials file rather than assuming its on the lead unit.

zaza/openstack/charm_tests/vault/utils.py

@@ -159,6 +159,22 @@ def ensure_secret_backend(client):
         pass
 
 
+def find_unit_with_creds():
+    """Find the unit thats has stored the credentials.
+
+    :returns: unit name
+    :rtype: str
+    """
+    unit = None
+    for vault_unit in zaza.model.get_units('vault'):
+        cmd = 'ls -l ~ubuntu/{}'.format(AUTH_FILE)
+        resp = zaza.model.run_on_unit(vault_unit.name, cmd)
+        if resp.get('Code') == '0':
+            unit = vault_unit.name
+            break
+    return unit
+
+
 def get_credentails():
     """Retrieve vault token and keys from unit.
 
@@ -168,7 +184,7 @@ def get_credentails():
     :returns: Tokens and keys for accessing test environment
     :rtype: dict
     """
-    unit = zaza.model.get_first_unit_name('vault')
+    unit = find_unit_with_creds()
     with tempfile.TemporaryDirectory() as tmpdirname:
         tmp_file = '{}/{}'.format(tmpdirname, AUTH_FILE)
         zaza.model.scp_from_unit(