Properly handle authentication with Keystone v3

Address few previously unnoticed use cases.
- Use uri_v3 is available (in the Tempest plugin). When v2
  is not available (as in modern deployments) the old value
  cannot be relied upon.
- Otherwise just check whether v3 is there and adds it if not
  (as it happens for example on a TripleO deployment).

Change-Id: I593faafbe6b4c547db687d4f521e2a0b412d343a

releasenotes/notes/more-auth-fixes-9ba23ceb54ba042a.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Properly handle more use cases when only Keystone v3 is enabled and/or
+    its service URI is missing the /v3 suffix.

sahara_tempest_plugin/tests/clients/base.py

@@ -46,11 +46,11 @@ class BaseDataProcessingTest(tempest.test.BaseTestCase):
 
         endpoint_type = TEMPEST_CONF.data_processing.endpoint_type
         catalog_type = TEMPEST_CONF.data_processing.catalog_type
-        auth_url = TEMPEST_CONF.identity.uri
+        auth_url = TEMPEST_CONF.identity.uri_v3
 
         credentials = cls.os_admin.credentials
 
-        auth = v3.Password(auth_url=auth_url.replace('/v2.0', '/v3'),
+        auth = v3.Password(auth_url=auth_url,
                            username=credentials.username,
                            password=credentials.password,
                            project_name=credentials.tenant_name,

sahara_tests/scenario/clients.py

@@ -39,7 +39,10 @@ from sahara_tests.scenario import utils
 
 def get_session(auth_url=None, username=None, password=None,
                 project_name=None, verify=True, cert=None):
-    auth = identity_v3.Password(auth_url=auth_url.replace('/v2.0', '/v3'),
+    auth_url_fixed = auth_url.replace('/v2.0', '/v3')
+    if not auth_url_fixed.endswith('/v3'):
+        auth_url_fixed += '/v3'
+    auth = identity_v3.Password(auth_url=auth_url_fixed,
                                 username=username,
                                 password=password,
                                 project_name=project_name,