hammerhead: Use less aggressive mount options

 * Reduce potential for FS corruption

Change-Id: I732ac0b4f91d7361a968e26e47ad3c02b2283c46
hammerhead: Optimize I/O scheduling

Inspired by bacon. We aren't suffering from slowdowns
during bootanim, anyway this is the right way to do it.

Change-Id: Icf3d9d6e52926012a4b7fdfdc1456a37ad782e71