Upgrade script to insert BOARD_USE into existing make.conf.board_setup files.
Upgrade script to insert BOARD_USE into existing make.conf.board_setup files.

The setup_board script now inserts a BOARD_USE value into
/build/<board>/etc/make.conf.board_setup.  This only happens the first
time the board is setup, so this upgrade script inserts that value
for boards that were previously set up.

BUG=chromium-os:20341
TEST=Ran run_chroot_version_hooks in chroot, inspected make.conf.board_setup
files for boards that did and did not have BOARD_USE already set.

Change-Id: I333198a0434076a5e8e50db6affc81ea2076d301
Reviewed-on: http://gerrit.chromium.org/gerrit/7653
Reviewed-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Tested-by: Matt Tennant <46e612415b446ccde19638e4035892001c237942@chromium.org>

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