Set bufsize to '-1' so we use io.DEFAULT_BUFFER_SIZE

- Removes RuntimeWarning: line buffering (buffering=1) isn't supported in binary mode, the default buffer size will be used

Signed-off-by: Thomas Lauf <thomas.lauf@tngtech.com>

test/basetest/utils.py

@@ -222,7 +222,7 @@ def run_cmd_wait(cmd, input=None, stdout=PIPE, stderr=PIPE,
             "stdin": stdin,
             "stdout": stdout,
             "stderr": stderr,
-            "bufsize": 1,
+            "bufsize": -1,
             "close_fds": ON_POSIX,
             "env": env,
         },