tools/mpremote: Make sure stdout and stderr output appear in order.

mpremote error messages now go to stderr, so make sure stdout is flushed
before printing them.

Also update the test runner to capture error messages.

Signed-off-by: Damien George <damien@micropython.org>

tools/mpremote/mpremote/main.py

@@ -547,7 +547,10 @@ def main():
 
         return 0
     except CommandError as e:
+        # Make sure existing stdout appears before the error message on stderr.
+        sys.stdout.flush()
         print(f"{_PROG}: {e}", file=sys.stderr)
+        sys.stderr.flush()
         return 1
     finally:
         do_disconnect(state)

tools/mpremote/tests/run-mpremote-tests.sh

@@ -16,7 +16,7 @@ for t in $TESTS; do
     TMP=$(mktemp -d)
     echo -n "${t}: "
     # Strip CR and replace the random temp dir with a token.
-    if env MPREMOTE=${MPREMOTE} TMP="${TMP}" "${t}" | tr -d '\r' | sed "s,${TMP},"'${TMP},g' > "${t}.out"; then
+    if env MPREMOTE=${MPREMOTE} TMP="${TMP}" "${t}" 2>&1 | tr -d '\r' | sed "s,${TMP},"'${TMP},g' > "${t}.out"; then
         if diff "${t}.out" "${t}.exp" > /dev/null; then
             echo "OK"
         else