Update test to fail instead of skip if floating pool is already allocated

The FloatingIPsBulkAdminTestJSON skips instead of fail if the pool is already configured.
This patch updates the test to fail when the floating pool is found to be already configured.

Change-Id: Iee5317c174c9abfc3514b6833d35e17969b15693
Closes-Bug: #1401280
diff --git a/tempest/api/compute/admin/test_floating_ips_bulk.py b/tempest/api/compute/admin/test_floating_ips_bulk.py
index 7ca081a..aa71665 100644
--- a/tempest/api/compute/admin/test_floating_ips_bulk.py
+++ b/tempest/api/compute/admin/test_floating_ips_bulk.py
@@ -17,6 +17,7 @@
 
 from tempest.api.compute import base
 from tempest import config
+from tempest import exceptions
 from tempest import test
 
 CONF = config.CONF
@@ -47,7 +48,7 @@
                 msg = ("Configured unallocated floating IP range is already "
                        "allocated. Configure the correct unallocated range "
                        "as 'floating_ip_range'")
-                raise cls.skipException(msg)
+                raise exceptions.InvalidConfiguration(msg)
         return
 
     def _delete_floating_ips_bulk(self, ip_range):