Added new test case to SNMP-Alerts submenu

Changes:
    - Added test to configure SNMP manager with empty IP,
      negative IPand alphanumeric port and verify

Tested:
    - Ran successfully test_snmp_alerts_sub_menu.robot

Change-Id: I4a8be9c63e426d22e131216c1817a3b83a2d5e9d
Signed-off-by: Megha G N <Megha.G.N@ibm.com>
diff --git a/lib/snmp/resource.robot b/lib/snmp/resource.robot
index d2493b5..eadf82f 100644
--- a/lib/snmp/resource.robot
+++ b/lib/snmp/resource.robot
@@ -11,6 +11,8 @@
 ${out_of_range_ip}    10.6.6.256
 ${alpha_ip}           xx.xx.xx.xx
 ${less_octet_ip}      10.5.5
+${negative_ip}        -10.6.6.6
+${empty_ip}           ${EMPTY}
 
 # Valid and invalid IP and ports. Valid port range is 0-65535.
 # Default port is 162.
@@ -22,6 +24,7 @@
 ${alpha_port}         ab
 ${negative_port}      ${-12}
 ${empty_port}         ${EMPTY}
+${alphanumeric_port}  abc123
 
 # User Name Password
 ${SNMP_MGR1_USERNAME}    ${EMPTY}