Enhanced User Management page error message

Description 1:
When WebUI creates the user with an already existing username
the error message will display the exact failure reason.

Tested:
Step 1: Login to webUI and navigate to user management page
Step 2: Create new user with username "testUser1"
Step 3: Create another user with same username "testUser1"
Step 4: WEB UI will through the error message
as "Username 'testuser1' already exists."

Description 2:
User can able to disable and change the root user via WebUI
Now restricted to disable the root user and changing the
root user privilege.

Tested:
Step 1: Login to Web UI with root user
Step 2: Navigate to User management page
Step 3: Try to modify the root user's details
Step 4: WebUI won't allow to disable the user,
username change and privilege change
Step 5: Login Web UI with non-root user
Step 6: Web UI won't allow to modify or delete the root
user's details

Change-Id: I0e38215b51fb058984664ec38ae9613e18043ed7
Signed-off-by: Sivaprabu Ganesan <sivaprabug@ami.com>
diff --git a/src/locales/en-US.json b/src/locales/en-US.json
index ffb6a2e..0796c67 100644
--- a/src/locales/en-US.json
+++ b/src/locales/en-US.json
@@ -581,6 +581,7 @@
             "errorBatchDisable": "Error disabling %{count} user. | Error disabling %{count} users.",
             "errorBatchEnable": "Error enabling %{count} user. | Error enabling %{count} users.",
             "errorCreateUser": "Error creating user '%{username}'.",
+            "errorAlreadyExistUser": "Username '%{username}' already exists.",
             "errorDeleteUser": "Error deleting user '%{username}'.",
             "errorLoadAccountSettings": "Error loading account settings",
             "errorLoadUsers": "Error loading users.",