remount: Factor some code out of fs_mgr_overlayfs_mount_all().

To ease on the indentation, this factors the innermost code of
overlayfs_mountall() into a new TryMountScratch() function.

Bug: 134949511
Test: adb remount
Change-Id: I894cbcd17bb6bd64751f235a074fa5ba7ce5157c
1 file changed