get_hd_serial is not used anywhere, so stay with get_hd_info.

Improve non-root usage:
 - optionally use different config files via MDADM_CONF_BASE env
 - correctly honor verbose setting in MxRaid::HostData

To use nvme 'disks' as journal device mxraid_assemble needs to
be aware of partitioned devices.

Partitions are addressed by adding '.PartId' to the serial number
in mxmd.conf (see full explanation there).

Rationale: Adding/removing an external journal to/from a md
device requires a couple of mdadm commands that are not that
straight forward.

Given that there are no open files on the md device, switching is
accomplished with:

  #> mxraid_journal journal md0 nvme0n1p1

And in the other direction:

  #> mxraid_journal bitmap md0