qemu-iotests: Add supported os parameter for python tests

If I understand correctly, qemu-iotests never meant to be portable. We
only support Linux for all the shell cases, but didn't specify it for
python tests. Now add this and default all the python tests as Linux
only. If we cares enough later, we can override the parameter in
individual cases.

Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

tests/qemu-iotests/iotests.py

@@ -282,12 +282,15 @@ def notrun(reason):
     print '%s not run: %s' % (seq, reason)
     sys.exit(0)
 
-def main(supported_fmts=[]):
+def main(supported_fmts=[], supported_oses=['linux']):
     '''Run tests'''
 
     if supported_fmts and (imgfmt not in supported_fmts):
         notrun('not suitable for this image format: %s' % imgfmt)
 
+    if sys.platform not in supported_oses:
+        notrun('not suitable for this OS: %s' % sys.platform)
+
     # 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