contrib/onie-server: find all IPs assigned

Finds all IPv4 addresses assigned to the box by running 'ifconfig' and
friends, depending on the OS we are running on. In addition the IP
addresses found are filtered to remove IPs that begin with '127.*' and
'169.254.*'.

Signed-off-by: Jonathan Toppins <jtoppins@cumulusnetworks.com>