Change manila_tempest_tests to use credentials_factory

With the merge of 'Factor up config dependent credential classes' in tempest,
(Change-Id: I351f86f0570070105bbf24f2d904e917feea6e57)
helper methods related to credentials have been moved to
common.credentials_factory module.
manila_tempest_tests need to change accordingly.

Change-Id: I9e5c72279638e07f509a4bfe0174b5ad5ee70b45
Closes-Bug: #1519612
diff --git a/manila_tempest_tests/tests/api/base.py b/manila_tempest_tests/tests/api/base.py
index b2da080..1fe3a4d 100644
--- a/manila_tempest_tests/tests/api/base.py
+++ b/manila_tempest_tests/tests/api/base.py
@@ -21,6 +21,7 @@
 from oslo_concurrency import lockutils
 from oslo_log import log
 import six
+from tempest.common import credentials_factory as common_creds
 from tempest.common import dynamic_creds
 from tempest import config
 from tempest import test
@@ -132,7 +133,9 @@
         ic = dynamic_creds.DynamicCredentialProvider(
             identity_version=CONF.identity.auth_version,
             name=name,
-            admin_role=CONF.identity.admin_role)
+            admin_role=CONF.identity.admin_role,
+            admin_creds=common_creds.get_configured_credentials(
+                'identity_admin'))
         if "admin" in type_of_creds:
             creds = ic.get_admin_creds()
         elif "alt" in type_of_creds:
@@ -269,7 +272,8 @@
                         identity_version=CONF.identity.auth_version,
                         name=service_net_name,
                         admin_role=CONF.identity.admin_role,
-                    )
+                        admin_creds=common_creds.get_configured_credentials(
+                            'identity_admin'))
                     net_data = ic._create_network_resources(sc.tenant_id)
                     network, subnet, router = net_data
                     net_id = network["id"]