cros_make_image_bootable: Do a final sanity check on the rootfs by running e2fsck
cros_make_image_bootable: Do a final sanity check on the rootfs by running e2fsck

This is a complement to the proposed fix for http://crosbug.com/9447, and I am getting it out first since it is a relatively simple change.

This change ensures that the rootfs on the image output by cros_make_image_bootable wasn't corrupted accidentally (for example, no boot.desc was provided and the defaults were incorrect for the image). This should catch rootfs errors that we end up discovering at delta AU time.

BUG=chromium-os:9578
TEST= Ran cros_make_image_bootable manually on an existing image with and without boot.desc. As expected, without boot.desc the output image rootfs had errors.

Also ran ./build_image - which worked fine too.

Change-Id: I4ed3a56634f37ab7d5ff2dc052ad607740356a40

Review URL: http://codereview.chromium.org/5216003

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