Clean up existing instances when not using tenant isolation

The test_list_servers_negative tests require that there are no existing
instances in the database when they run and will fail if any are found
under the primary/alternate user/tenant.

When running tempest with allow_tenant_isolation=false on a slower
system, there is a race where instances from previous tests are still
cleaning up in the background and cause test_list_servers_negative to
fail in setup.

This patch makes test_list_servers_negative block while the deleted
instances are being cleaned up in the background if running without
tenant isolation.

Closes-Bug: #1234370

Change-Id: I8519cba1fcf6ff39d69839783d07359544509db5

tempest/api/compute/servers/test_list_servers_negative.py

@@ -27,6 +27,26 @@ from tempest.test import attr
 class ListServersNegativeTestJSON(base.BaseComputeTest):
     _interface = 'json'
 
+    @classmethod
+    def _ensure_no_servers(cls, servers, username, tenant_name):
+        """
+        If there are servers and there is tenant isolation then a
+        skipException is raised to skip the test since it requires no servers
+        to already exist for the given user/tenant.
+        If there are servers and there is not tenant isolation then the test
+        blocks while the servers are being deleted.
+        """
+        if len(servers):
+            if not compute.MULTI_USER:
+                for srv in servers:
+                    cls.client.wait_for_server_termination(srv['id'],
+                                                           ignore_error=True)
+            else:
+                msg = ("User/tenant %(u)s/%(t)s already have "
+                       "existing server instances. Skipping test." %
+                       {'u': username, 't': tenant_name})
+                raise cls.skipException(msg)
+
     @classmethod
     def setUpClass(cls):
         super(ListServersNegativeTestJSON, cls).setUpClass()
@@ -54,26 +74,14 @@ class ListServersNegativeTestJSON(base.BaseComputeTest):
         # start of the test instead of destroying any existing
         # servers.
         resp, body = cls.client.list_servers()
-        servers = body['servers']
+        cls._ensure_no_servers(body['servers'],
-        num_servers = len(servers)
+                               cls.os.username,
-        if num_servers > 0:
+                               cls.os.tenant_name)
-            username = cls.os.username
-            tenant_name = cls.os.tenant_name
-            msg = ("User/tenant %(u)s/%(t)s already have "
-                   "existing server instances. Skipping test." %
-                   {'u': username, 't': tenant_name})
-            raise cls.skipException(msg)
 
         resp, body = cls.alt_client.list_servers()
-        servers = body['servers']
+        cls._ensure_no_servers(body['servers'],
-        num_servers = len(servers)
+                               cls.alt_manager.username,
-        if num_servers > 0:
+                               cls.alt_manager.tenant_name)
-            username = cls.alt_manager.username
-            tenant_name = cls.alt_manager.tenant_name
-            msg = ("Alt User/tenant %(u)s/%(t)s already have "
-                   "existing server instances. Skipping test." %
-                   {'u': username, 't': tenant_name})
-            raise cls.skipException(msg)
 
         # The following servers are created for use
         # by the test methods in this class. These