fsck rootfs before booting

The attached patch implements rootfs checking before booting. This is needed because rootfs has its journal disabled and unclean shutdowns always result in some filesystem damage, which may sometimes lead to data loss.

e2fsck binary is from 1.42.5-1ubuntu4 ubuntu e2fsprogs package (http://ports.ubuntu.com/pool/main/e/e2fsprogs/e2fsprogs_1.42.5-1ubuntu4_armhf.deb)