Get snmp/snmpd installed and wire up configs

Issue TA411
Attempt to move the debconf exim bits for rewrite/relay to the cent
exim.conf
Merge pull request #9 from claco/ta411-snmp

Get snmp/snmpd installed and wire up configs
Merge pull request #10 from claco/rhel-exim-config

cent exim.conf tweakings