Merge "fs_mgr: move mkdir(mount_point) to prepare_fs_for_mount()" am: a1411e4311 am: 9ed5699204

Original change: https://android-review.googlesource.com/c/platform/system/core/+/1505939

Change-Id: I0cdaa53787b0b2ebd4082950a33e7d43e958dd38