ifupdown2 behaviour significantly diverges from ifupdown on debian stretch.
Original ifupdown uses run-parts which supposedly doesn't run non-executable
files in the directory. However, ifupdown2 doesn't seem to make this
distinction.
This patch will log warning EACCES exceptions (instead of log error) and exit 0
Reported-by: George Diamantopoulos <gedia>
Signed-off-by: Julien Fortin <julien@cumulusnetworks.com>