Clarify extra vars are not passed with -e

When we made this change the release notes made note of it, but the docs
for the extra vars job attribute did not. Update the job attribute docs
to clarify this behavior as well to avoid any confusion.

Change-Id: I83b5f7c0a26ffb40e413e02ad2463434e5780fc5

doc/source/config/job.rst

@@ -719,7 +719,9 @@ Here is an example of two job definitions:
    .. attr:: extra-vars
 
       A dictionary of variables to supply to Ansible with higher
-      precedence than job, host, or group vars.
+      precedence than job, host, or group vars. Note, that despite
+      the name this is not passed to Ansible using the `--extra-vars`
+      flag.
 
    .. attr:: host-vars