Don't fsck during shutdown.

Ie1b1492910ea0291680739770a6b44e384890391 removed fsck for f2fs. This
change does the same for ext4, removing fsck completely during shutdown.

In addition to this, during boot, for ext4, run e2fsck with -p (preen /
autorepair) when fsck is not forced. Previously it ran with -y which
runs "all" checks and thus usually takes longer than -p.

We now run e2fsck with -y only when e2fsck -p failed with uncorrected
errors or the check is forcibly requested (ex: mount failed).

Bug: 432462088
Test: Run the following with and without this change.
for i in {1..10}; do \
adb reboot; \
adb wait-for-device; \
adb root; \
adb shell getprop ro.boottime.init.fsck.data; \
done

and take the average.
With this change: 12ms
Without this change: 13ms

This was measured on CF with relatively clean /data.
Flag: EXEMPT bug fix

Change-Id: Ibb8d7b5065b45f7ea052dd2d6d8f7291d350131c