trace: SystemTap documentation out of date

[Philippe Mathieu-Daudé]

The docs/devel/tracing.txt help suggest:

    scripts/tracetool.py --backends=dtrace --format=stap \
                         --binary path/to/qemu-binary \
                         --target-type system \
                         --target-name x86_64 \
                         <trace-events-all >qemu.stp

but since commit 2098c56a9bc this comment is outdated:

  $ scripts/tracetool.py --backends=dtrace --format=stap \
    --binary mips-softmmu/qemu-system-mips \
    --target-type system \
    --target-name mips trace-events-all
  Error: group name is required

The offending commit seems:

commit 2098c56a9bc5901e145fa5d4759f075808811685
Author: Daniel P. Berrange <email address hidden>
Date: Wed Jan 25 16:14:14 2017 +0000

    trace: move setting of group name into Makefiles

[Philippe Mathieu-Daudé (philmd)]

Fixed by commit bd200384c515 (trace: add --group=all to tracing.txt).

[Philippe Mathieu-Daudé (philmd)]

Fixed in v4.2.0.