Fix rebuild blacklist so that icedtea isn't rebuilt unnecessarily.
Fix rebuild blacklist so that icedtea isn't rebuilt unnecessarily.

It turns out that my previous rebuild_blacklist code had a bug where
blacklisted packages would get rebuilt unnecessarily. This would result
in slow builds if icedtea was built.

BUG=chromium-os:6628
TEST=Mock case where prebuilts for icedtea are older than packages that
     icedtea depends on.

Change-Id: I498b6499b78ab065109c1fe0e77969028ceff6cb

Review URL: http://codereview.chromium.org/3308027

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