lshal: Add fqname to debug error messages

If any error comes up when invoking debug, write fqname and the error
message to the error output stream.

Test: manual. Add addPostCommandTask to a HAL that keeps writing to the
fd after debug() finishes. lshal debug terminates with fqname and
the error message `timeout reading from pipe, output may be truncated.`

Fixes: 169247570

Change-Id: Idf8944e3cde08dc86766b144c4a3037cbcf6b3dc