fs_mgr: overlayfs: noatime

Should not have used relatime for overlayfs and backing storage
mounts, noatime reduces the wear and tear on the flash device.

This should prevent triggering a falure in the CtsOsTestCases that
tries to spot mounts attached to block storage from updating atime
and resulting in churn.  This statement does not mean we support
performing Cts tests with devices that have deployed
'adb disable-verity' or 'adb remount'.

Post-mortem: relatime was not a 'problem' for overlayfs, copy and
             paste for those flags resulted in the use of relatime
	     for scratch backing storage.

Test: adb-remount-test.sh
Bug: 140014856
Change-Id: Ic97b98ceacaa265094364487ea70cc99b6aee92f