cros_workon: quick hack at package name checking
cros_workon: quick hack at package name checking

Change-Id: I30e97760d5b96077e38414be31ef434542021361

Review URL: http://codereview.chromium.org/2883012

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