Print "(repairing)" in zpool status again

Historically, zpool status prints "(repairing)" for any drives that
have errors during a scrub:

        NAME            STATE     READ WRITE CKSUM
        mypool          ONLINE       0     0     0
          mirror-0      ONLINE       0     0     0
            /tmp/file1  ONLINE      13     0     0  (repairing)
            /tmp/file2  ONLINE       0     0     0
            /tmp/file3  ONLINE       0     0     0

This was accidentally broken in "OpenZFS 9166 - zfs storage pool
checkpoint" (d2734cc). This patch adds it back in.

Reviewed-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #7779
Closes #7978