Updated openstack/openstack
Project: openstack-dev/devstack  f8afb8bee1de1ccad21c71abb5ba0b1f54296a02
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remove additional f18 references

f18 has been EOL for 6 weeks now, time to purge it from devstack

Change-Id: I5aac2c63b2f4cd8b01ae685b1acf4c188637558b