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/gui/lib/gui_resource.robot b/gui/lib/gui_resource.robot
index 81216f8..391839d 100644
--- a/gui/lib/gui_resource.robot
+++ b/gui/lib/gui_resource.robot
@@ -90,9 +90,9 @@
     # password  The password to be used for login.
 
     Go To  ${obmc_gui_url}
-    Wait Until Element Is Enabled  ${xpath_textbox_username}
-    Input Text  ${xpath_textbox_username}  ${username}
-    Input Password  ${xpath_textbox_password}  ${password}
+    Wait Until Element Is Enabled  ${xpath_login_username_input}
+    Input Text  ${xpath_login_username_input}  ${username}
+    Input Password  ${xpath_login_password_input}  ${password}
     Click Element  ${xpath_login_button}
     Wait Until Page Contains  Overview  timeout=60s