iotests.py: s/_/-/g on keys in qmp_log()

This follows what qmp() does, so the output will correspond to the
actual QMP command.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190210145736.1486-11-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
8 files changed