Handle virtio in private fs mapping

Handle virtio in private fs mapping

When the vold core decides if a device is SD or USB, it checks for MMC
or virtio, however when the filesystem type is decided, it does not
check for virtio, only MMC. This causes virtio SD cards to be formatted
with ext4 unconditionally.

This fix is independently correct, but it incidentally gets adopted
storage working on cuttlefish (and Android Emulator) because f2fs can
support fscrypt and casefolding at the same time; ext4 currently cannot.

Bug: 156286088
Change-Id: I0b41670d5f76b2506dad437917c2276f8e0aaccf