[Qemu-block] [PATCH v3] python: Use io.StringIO

[Philippe Mathieu-Daudé]

Both Python 2.7 and 3 support the same io.StringIO to
handle unicode strings.

Use the common form to use indistinctly Python 2.7 or 3.

http://python-future.org/compatible_idioms.html#stringio

This fixes running tests on the Fedora Docker image,
which uses Python3 since 356dc290f:

  $ make address@hidden
  [...]
  045         [failed, exit status 1] - output mismatch (see 045.out.bad)
  --- /tmp/qemu-test/src/tests/qemu-iotests/045.out       2018-07-17 
16:56:18.000000000 +0000
  +++ /tmp/qemu-test/build/tests/qemu-iotests/045.out.bad 2018-07-17 
17:19:22.448409007 +0000
  @@ -1,5 +1,6 @@
  -...........
  -----------------------------------------------------------------------
  -Ran 11 tests
  -
  -OK
  +Traceback (most recent call last):
  +  File "045", line 178, in <module>
  +    iotests.main(supported_fmts=['raw'])
  +  File "/tmp/qemu-test/src/tests/qemu-iotests/iotests.py", line 682, in main
  +    import StringIO
  +ModuleNotFoundError: No module named 'StringIO'
  132         [failed, exit status 1] - output mismatch (see 132.out.bad)
  152         [failed, exit status 1] - output mismatch (see 152.out.bad)

  Failures: 045 132 152

Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
---
 tests/qemu-iotests/iotests.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
index 4e67fbbe96..cd9be1bd9c 100644
--- a/tests/qemu-iotests/iotests.py
+++ b/tests/qemu-iotests/iotests.py
@@ -679,13 +679,13 @@ def main(supported_fmts=[], supported_oses=['linux'], 
supported_cache_modes=[],
 
     # We need to filter out the time taken from the output so that qemu-iotest
     # can reliably diff the results against master output.
-    import StringIO
+    from io import StringIO
     if debug:
         output = sys.stdout
         verbosity = 2
         sys.argv.remove('-d')
     else:
-        output = StringIO.StringIO()
+        output = StringIO()
 
     logging.basicConfig(level=(logging.DEBUG if debug else logging.WARN))
 
-- 
2.19.1