With [1] the devstack zuul job will try to update Neutron's
configuration, even though we don't use Neutron for Qinling at all.
This commit is a workaround to create a Neutron config dir to satisfy
devstack when the Neutron service is actually disabled.
[1] I2dcbd9bdb401860820e655d97aa3c4775af2827f
Change-Id: I6ecc7d631c7deccf7d5011ec68a08759441a0318