Skip xml test test_pool_scheduling_on_pool_creation

This patch causes the above test to be skipped as it has caused the havana
tests on the gate to be broken for a few weeks now. Since XML support doesn't
fully work in neutron and marked to be removed in juno skipping this xml test
should be okay.

Change-Id: I06e3eb08f6d53332267fd181c603b138bd4d8c01
Related-bug: 1311232