add :0 as port when sending outgoing SNMP requests

so that non-root users can bind to it and we avoid getting
SNMP permission denied errors when icinga
runs these.

we send the client IP since I9c7b1c11aeef2ff984ab25c7c81514be3c5897db

this fixes lots of Icinga monitors with status UNKNOWN

https://icinga.wikimedia.org/cgi-bin/icinga/status.cgi?host=all&type=detail&servicestatustypes=8&hoststatustypes=3&serviceprops=2097162&nostatusheader

if snmp.conf just has the IP:  clientaddr 208.80.154.14

root@neon:~# sudo -u nagios /usr/lib/nagios/plugins/check_snmp -H 10.65.0.42 -C ...
External command error: snmpget: Unknown host (10.65.0.42:161) (Permission denied)

if snmp.conf also has port :0

root@neon:~# sudo -u nagios /usr/lib/nagios/plugins/check_snmp -H 10.65.0.42 -C ...
SNMP OK - ps1-b3-eqiad-infeed-load-tower-A-phase-X 750 | ps1-b3-eqiad-infeed-load-tower-A-phase-X=750

Change-Id: I2e8b31459e78e5fd743cc817faeab82971aa1e26
Merge "add :0 as port when sending outgoing SNMP requests" into production