[PATCH] python: fix Popen.wait() deadlock issue

[joeg at catalyst.net.nz]

Hi everyone,
I am Joe Guo, a new Samba developer from Catalyst IT, New Zealand.

In `python/samba/tests/__init__.py` file,  both `check_exit_code` and
`check_output` used `Popen.wait()` for command line output.
This will cause deadlock if the output is too large (for example, more
than 64k).

The issue is documented in Python official document at:
https://docs.python.org/2/library/subprocess.html#subprocess.Popen.wait

I created 2 patches for this issue.
0001 is the proof.  I added a python script to generate large output and
a known failed test case.
0002 is the fix. I use `communicate` instead of `wait` to avoid the
deadlock issue.


Cheers,
Joe Guo
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