setup_board: Move PFQ prebuilt URLs from chromeos-overlay to chromeos-partner-overlay.
setup_board: Move PFQ prebuilt URLs from chromeos-overlay to chromeos-partner-overlay.

This change makes it possible for partners to access internal prebuilts.
Note that partners will only have access to the actual prebuilts referenced
here if they have access to the right Google Storage key, which are stored
in the overlays themselves.

BUG=chrome-os-partner:7186, chromium-os:17346
TEST=Verify that setup_board now pulls internal prebuilts from chromeos-partner-overlay
     instead of chromeos-overlay.
CQ-DEPEND=13071

Change-Id: Ia5220002a18593e614ee67ccad16bb295c8b6d0b
Reviewed-on: https://gerrit.chromium.org/gerrit/13072
Reviewed-by: Ryan Cui <5ce1592d53754a87a44fc2eb7b63d5f77cf50fdb@chromium.org>
Tested-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>

BugRoger/scripts,sigma/coreos-scripts,crawford/scripts,marineam/coreos-scripts,endocode/scripts,smilart/scripts,vmware/coreos-scripts,glevand/coreos--scripts,andrejro/coreos--scripts,bcwaldon/coreos-scripts,marineam/coreos-scripts,coreos/scripts,vmware/coreos-scripts,crawford/scripts,andrejro/coreos--scripts,mjg59/scripts,endocode/scripts,smilart/scripts,nicescale/scripts,mischief/scripts,endocode/scripts,nicescale/scripts,fivethreeo/scripts,sigma/coreos-scripts,bcwaldon/coreos-scripts,BugRoger/scripts,coreos/scripts,zhang0137/scripts,zhang0137/scripts,fivethreeo/scripts,crawford/scripts,BugRoger/scripts,andrejro/coreos--scripts,vmware/coreos-scripts,gtank/scripts,nicescale/scripts,sigma/coreos-scripts,glevand/coreos--scripts,mjg59/scripts,fivethreeo/scripts,zhang0137/scripts,gtank/scripts,gtank/scripts,trnubo/scripts,bcwaldon/coreos-scripts,mischief/scripts,trnubo/scripts,mjg59/scripts,mischief/scripts,marineam/coreos-scripts,trnubo/scripts,smilart/scripts