discover/udev: Additional checks in udev_handle_block_add
- Several filesystem types can appear that we won't be able to mount.
Instead of waiting to fail mounting them in device_handler_discover(),
skip processing them at all.
- Do not create dm-snapshots on top of raid arrays until we have a
reliable way of determining the sector count for a md raid device.
- Turn down the verbosity on skipping dm-devices.
Signed-off-by: Samuel Mendoza-Jonas <sam.mj@au1.ibm.com>