Make ROOT-B 4096 blocks long to workaround recovery image padding
Make ROOT-B 4096 blocks long to workaround recovery image padding

BUG=chrome-os-partner:15036
TEST=Build/run recovery image, verify it runs at expected speed

Change-Id: I8bd701761456a9444845ffc87b9b70f7d3f0c371
Reviewed-on: https://gerrit.chromium.org/gerrit/35226
Reviewed-by: Don Garrett <546ec366615570e68497e3c5df9092106a9808f4@chromium.org>
Commit-Ready: Liam McLoughlin <a63c1d66dbd75d3cc434e11bdf376be6f9ff043b@chromium.org>
Tested-by: Liam McLoughlin <a63c1d66dbd75d3cc434e11bdf376be6f9ff043b@chromium.org>

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