PhysicalConsole: Fix UTF-8 related failure

[zmc]

This is a re-file of #1879.

Fixes: https://tracker.ceph.com/issues/62286

@dmick, I'm not sure if this was your intent, but we're logging a lot more now after #1869. For example:

$ grep -a -A1 "console.*\(expect before\|output\):" /a/zack-2023-08-02_18:04:55-powercycle-reef-distro-default-smithi/7358307/teuthology.log > /tmp/7358307_console.txt
$ wc -l /tmp/7358307_console.txt
76 /tmp/7358307_console.txt
$ wc -c /tmp/7358307_console.txt
53344 /tmp/7358307_console.txt53344

[dmick]

Yes, the excess logging is intentional. We don't have a clue why ipmitool is failing sometimes, so I'm attempting to find that out.

[dmick]

makes sense to me