autotest: don't wipe FEATURES when building
autotest: don't wipe FEATURES when building

Review URL: http://codereview.chromium.org/866001

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