trace: update qemu-trace-stap to Python 3

trace: update qemu-trace-stap to Python 3

qemu-trace-stap does not support Python 3 yet:

  $ scripts/qemu-trace-stap list path/to/qemu-system-x86_64
  Traceback (most recent call last):
    File "scripts/qemu-trace-stap", line 175, in <module>
      main()
    File "scripts/qemu-trace-stap", line 171, in main
      args.func(args)
    File "scripts/qemu-trace-stap", line 118, in cmd_list
      print_probes(args.verbose, "*")
    File "scripts/qemu-trace-stap", line 114, in print_probes
      if line.startswith(prefix):
  TypeError: startswith first arg must be bytes or a tuple of bytes, not str

Now that QEMU requires Python 3.5 or later we can switch to pure Python
3.  Use Popen()'s universal_newlines=True argument to treat stdout as
text instead of binary.

Fixes: 62dd1048c0bd ("trace: add ability to do simple printf logging via systemtap")
Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1787395
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20200107112438.383958-1-stefanha@redhat.com
Message-Id: <20200107112438.383958-1-stefanha@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>