iotests.py: Filter filename in any string value

iotests.py: Filter filename in any string value

filter_qmp_testfiles() currently filters the filename only for specific
keys.  However, there are more keys that take filenames (such as
block-commit's @top and @base, or ssh's @path), and it does not make
sense to list them all here.  "$TEST_DIR/$PID-" should have enough
entropy not to appear anywhere randomly.

Signed-off-by: Max Reitz <[email protected]>
Reviewed-by: John Snow <[email protected]>
Message-id: 20190210145736[email protected]
Signed-off-by: Max Reitz <[email protected]>