ENH: set user realm when chaning passwords

This is a MR for #133 (closed) .

I think this change could be useful, see my comment in #133 (closed) : #133 (comment 75953)

src/linkahead/utils/linkahead_admin.py

@@ -42,6 +42,13 @@ __updated__ = '2018-12-11'
 
 
 def do_update_role(args):
+    """
+    Update the description of a role.
+
+    Allowed keyword arguments:
+    role_name: Name of the role to update
+    role_description: New description of the role
+    """
     admin._update_role(name=args.role_name, description=args.role_description)
 
 
@@ -123,7 +130,6 @@ def do_create_user(args):
     try:
         admin._insert_user(name=args.user_name,
                            email=args.user_email, password=password)
-
         if args.activate_user:
             do_activate_user(args)
     except HTTPClientError as e:
@@ -150,7 +156,7 @@ def do_set_user_password(args):
     else:
         password = args.user_password
     try:
-        admin._update_user(name=args.user_name, password=password)
+        admin._update_user(name=args.user_name, password=password, realm=args.realm)
     except HTTPClientError as e:
         print(e.msg)
 
@@ -364,6 +370,12 @@ USAGE
         metavar='USERNAME',
         dest="user_name",
         help="The name of the user who's password is to be set.")
+    subparser.add_argument(
+        metavar='REALM',
+        dest="realm",
+        nargs="?",
+        default=None,
+        help="The realm of the user who's password is to be set.")
     subparser.add_argument(
         metavar='PASSWORD',
         nargs="?",