Add more choices to grub2 menu.
Add more choices to grub2 menu.

This adds some '/dev/sdb' options to the grub2 menu, so that we can keep the
default boot partition /dev/sda3 while still using the USB key as a recovery
image. This is work in progress for EFI BIOS development.

Review URL: http://codereview.chromium.org/1706014

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