Added new SNMP testcase

Changes :
    - Configure SNMP Manager With Hostname Via GUI AND Verify
    - Removed "Add DNS Servers And Verify" keyword from test_network_sub_menu.robot
      and added in lib file gui_resource.robot

Tested:
    - Ran successfully test_snmp_alerts_sub_menu.robot

Change-Id: Ib6e90c8ae45d1185631416e83144d739f0d8c38a
Signed-off-by: Megha G N <Megha.G.N@ibm.com>
diff --git a/gui/data/gui_variables.py b/gui/data/gui_variables.py
index 107885e..8d15e39 100644
--- a/gui/data/gui_variables.py
+++ b/gui/data/gui_variables.py
@@ -71,6 +71,14 @@
     xpath_power_restore_policy_sub_menu = (
         "//*[@data-test-id='nav-item-power-restore-policy']"
     )
+    xpath_static_dns = "//h2[text()='Static DNS']"
+    xpath_dns_servers_toggle = (
+        "//*[@data-test-id='networkSettings-switch-useDns']"
+    )
+    xpath_add_dns_ip_address_button = (
+        "//button[contains(text(),'Add IP address')]"
+    )
+    xpath_input_static_dns = "//*[@id='staticDns']"
 
     # Security and access menu
     xpath_secuity_and_accesss_menu = (