automerge: make error-message formatting less amusing. (#35)

The automerge script failed just now (for a benign transient reason),
and printed this:

ERROR: Failed to run command: "[ ' g i t ' , ' - C ' , ' / h o m e / r u
n n e r / w o r k / a r m - t o o l c h a i n / a r m - t o o l c h a i
n ' , ' p u s h ' , ' o r i g i n ' , ' a r m - s o f t w a r e ' ]"

because `error.cmd` was a list of strings, and the error message tried
to format it using `" ".join(str(error.cmd))`, which first converted the
list into a single string the same way `__repr__` would have done it
(displaying the list in Python syntax with strings quoted), and then
applied `" ".join` to the resulting string, which caused it to be
treated as a list of characters, and each pair of characters separated
with a space.

The sensible way to format a shell command in list-of-strings format is
`shlex.join`. Funny as the above is, let's use that instead :-)

Author: statham-arm

arm-software/ci/automerge.py

@@ -8,6 +8,7 @@
 import argparse
 import json
 import logging
+import shlex
 import subprocess
 import sys
 from pathlib import Path
@@ -206,7 +207,7 @@ def main():
     except subprocess.CalledProcessError as error:
         logger.error(
             'Failed to run command: "%s"\nstdout:\n%s\nstderr:\n%s',
-            " ".join(str(error.cmd)),
+            shlex.join(error.cmd),
             error.stdout,
             error.stderr,
         )