AMBARI-26307: Knox SSO fails to login into Ambari

[prabhjyotsingh]

What changes were proposed in this pull request?

Fix getAuthenticated method when Knox SSO is enabled.
I believe this started happening after the jQuery upgrade.

How was this patch tested?

Have installed Knox in one of the hosts, then setup Knox SSO for Ambari (ambari-server setup-sso).
Once everything is configured/restarted check if we are able to login using knox-sso (hadoop-jwt) or not.

And without this patch UI errors out with

Uncaught TypeError: xhr.getResponseHeader is not a function
    at Class.<anonymous> (app.js:92484:24)
    at c (vendor.js:1717:25)
    at Object.fireWith [as resolveWith] (vendor.js:1772:20)
    at l (vendor.js:4936:19)
    at XMLHttpRequest.<anonymous> (vendor.js:5085:23)

[basapuram-kumar]

LGTM

[JiaLiangC]

@zRains Could you help review this?

[zRains]

cc @JiaLiangC