Network performance between hpcloud workers and servers in rax-dfw
have returned to acceptable levels, so return node labels and
max-servers counts to their previous values.
Also add the devstack-precise-check label back to work around
https://storyboard.openstack.org/#!/story/64 and temporarily leave
az1 and az2 out of the bare-centos6 set until Clark has an
opportunity to finish building updated images there.
Change-Id: Id1a89dff94b38c64f655577f0040bcc1f78aa479
0bdf4045aa