Clean existing SNMP manager daemons before starting SNMP manager

Changes:
    - Execute "killall snmptrapd" on the SNMP server.

Tested:
    redfish/events/test_bmc_snmp_trap.robot

Signed-off-by: Prashanth Katti <prkatti1@in.ibm.com>
Change-Id: Ie0b237bb456c81077a4f4b5ef9b22760febc405e
diff --git a/lib/snmp/redfish_snmp_utils.robot b/lib/snmp/redfish_snmp_utils.robot
index 6f3cc34..0c7cb52 100644
--- a/lib/snmp/redfish_snmp_utils.robot
+++ b/lib/snmp/redfish_snmp_utils.robot
@@ -252,6 +252,9 @@
     Open Connection And Log In  ${SNMP_MGR1_USERNAME}  ${SNMP_MGR1_PASSWORD}
     ...  alias=snmp_server  host=${SNMP_MGR1_IP}
 
+    # Clean SNMP managers running in the background.
+    SSHLibrary.Execute Command  killall snmptrapd
+
     # The execution of the SNMP_TRAPD_CMD is necessary to cause SNMP to begin
     # listening to SNMP messages.
     SSHLibrary.write  ${SNMP_TRAPD_CMD} &