fs_mgr: fs_mgr_overlayfs_mount_scratch try alternate

Harden fs_mgr_overlayfs_mount_scratch to try alternate filesystem
mount type just in case (f2fs <-> ext4).

Cleanup remove any unnecessary string literals.

Test: manual
Bug: 109821105
Change-Id: I36ea974ffeeae392553fff779939dc76a12ab96e
1 file changed