This commit adds some additional logic that falls back to using the
ifdown/ifup tools to restart networking. On Ubuntu 14.04, the init
script was designed to always fail to restart newtorking, so it needs
to use the ifdown/up tools instead. This commit will use the networking
init script as a last resort to restart networking, assuming other
commands haven't broken networking already.
https://bugs.launchpad.net/ubuntu/+source/ifupdown/+bug/1301015
1761e65f26