zed: Fix mpath autoreplace on Centos 7

A prior commit included a udev check for MPATH_DEVICE_READY to
determine if a path was multipath when doing an autoreplace:

    f2f6c18 zed: Misc multipath autoreplace fixes

However, MPATH_DEVICE_READY is not provided by the older version of
udev that's on Centos 7 (it is on Centos 8).

This patch instead looks for 'mpath-' in the UUID, which works on
both Centos 7 and 8.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #13222