fix snmp to work

Need clean /var/lib/net-snmp/snmpd.conf before configure snmp and
set iptables for snmp.

Change-Id: Idc32bd53cffd2ef93a60a06f8937a9a9ff4539a5
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1096164
Signed-off-by: hadong <hadong@redhat.com>