autotest: fix pexpect in python3

  In python3 pexpect wants by default a BytesIO stream as log buffer.
Otherwise it will (silently masked since we just return false)
  File "/usr/share/dpdk/test/autotest_runner.py", line 22, in wait_prompt
    child.sendline()
  File "/usr/lib/python3/dist-packages/pexpect/pty_spawn.py", line 555, in sendline
    return self.send(s + self.linesep)
  File "/usr/lib/python3/dist-packages/pexpect/pty_spawn.py", line 543, in send
    self._log(s, 'send')
  File "/usr/lib/python3/dist-packages/pexpect/spawnbase.py", line 126, in _log
    self.logfile.write(s)

We have plenty of other code writing and using this buffer.
So instead of changing the type and modifying many more places we tell the
spawn [1] method to encode things right away - then the rest behaves as it
did with python2.

[1]: https://pexpect.readthedocs.io/en/stable/api/pexpect.html#spawn-class

Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
---
 app/test/autotest_runner.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
  

On Thu, 2020-05-07 at 14:38 +0200, Christian Ehrhardt wrote:
> In python3 pexpect wants by default a BytesIO stream as log buffer.
> Otherwise it will (silently masked since we just return false)
>   File "/usr/share/dpdk/test/autotest_runner.py", line 22, in wait_prompt
>     child.sendline()
>   File "/usr/lib/python3/dist-packages/pexpect/pty_spawn.py", line 555, in sendline
>     return self.send(s + self.linesep)
>   File "/usr/lib/python3/dist-packages/pexpect/pty_spawn.py", line 543, in send
>     self._log(s, 'send')
>   File "/usr/lib/python3/dist-packages/pexpect/spawnbase.py", line 126, in _log
>     self.logfile.write(s)
> 
> We have plenty of other code writing and using this buffer.
> So instead of changing the type and modifying many more places we tell the
> spawn [1] method to encode things right away - then the rest behaves as it
> did with python2.
> 
> [1]: https://pexpect.readthedocs.io/en/stable/api/pexpect.html#spawn-class
> 
> Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
> ---
>  app/test/autotest_runner.py | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/app/test/autotest_runner.py b/app/test/autotest_runner.py
> index dfa5f2b2dd..92d4e6e41a 100644
> --- a/app/test/autotest_runner.py
> +++ b/app/test/autotest_runner.py
> @@ -84,7 +84,7 @@ def pool_init(queue, result_queue):
>          print("\n%s %s\n" % ("=" * 20, prefix), file=startuplog)
>          print("\ncmdline=%s" % cmdline, file=startuplog)
>  
> -        pool_child = pexpect.spawn(cmdline, logfile=startuplog)
> +        pool_child = pexpect.spawn(cmdline, logfile=startuplog, encoding='utf-8')
>  
>          # wait for target to boot
>          if not wait_prompt(pool_child):

Acked-by: Luca Boccassi <bluca@debian.org>