Updated variable names in below files

Changes :-

updated variable name as xpath_login_username_input => gui/lib/gui_resource.robot, gui/data/gui_variables.py and security/test_bmc_connections.robot
updated variable name as xpath_login_password_input => gui/data/gui_variables.py, gui/lib/gui_resource.robot and security/test_bmc_connections.robot
updated variable name as xpath_textbox_hostname => gui/data/gui_variables.py

Change-Id: Icc9c420fd53f785bf6178ca324b23de7ddbbf936
Signed-off-by: rramyasr-in <rramyasr@in.ibm.com>
diff --git a/security/test_bmc_connections.robot b/security/test_bmc_connections.robot
index f75e73b..bbc9eb7 100644
--- a/security/test_bmc_connections.robot
+++ b/security/test_bmc_connections.robot
@@ -308,8 +308,8 @@
 Login to GUI With Incorrect Credentials
     [Documentation]  Attempt to login to GUI as root, providing incorrect password argument.
 
-    Input Text  ${xpath_textbox_username}  root
-    Input Password  ${xpath_textbox_password}  incorrect_password
+    Input Text  ${xpath_login_username_input}  root
+    Input Password  ${xpath_login_password_input}  incorrect_password
     Click Button  ${xpath_login_button}
 
 Invalid Credentials Redfish Login Attempts