setup_board: move all wrapper gen code into one func
setup_board: move all wrapper gen code into one func

Makes the code flow easier to follow, and makes it easier to skip
wrapper generation if we so desire.

BUG=chromium-os:34519
TEST=`./setup_board --board=lumpy` output looked ok
TEST=`cbuildbot {x86,amd64,arm}-generic-full chromiumos-sdk` worked

Change-Id: Ie7a1d387fb21a495c6a2da2c9147587743240929
Reviewed-on: https://gerrit.chromium.org/gerrit/33485
Reviewed-by: Zdenek Behan <483cf2a9a4e071d4fd973db6a5a78c40f490667c@chromium.org>
Commit-Ready: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>

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