2FA: don't redirect back to login screen after entering incorrect 2FA code

##### ISSUE TYPE

* Improvement Request

##### COMPONENT NAME

~~~
UI
~~~

##### CLOUDSTACK VERSION

~~~
4.18
~~~

##### CONFIGURATION

##### OS / ENVIRONMENT

N/A

##### SUMMARY

After entry of an invalid 2FA code, the user gets redirected back to the login screen, instead of offering the user the possibility of entering a 2FA code again. There should be no need to go back to the login screen if the user already made it to the 2FA screen.

##### STEPS TO REPRODUCE

* enter invalid 2FA code in the 2FA entry screen after logging in
* get returned back to login screen

##### EXPECTED RESULTS

Go back to 2FA entry screen and let the user try again, or submit the 2fa code using AJAX and give instant feedback on the 2FA screen about the invalid code and stay on the 2FA code entry page.

##### ACTUAL RESULTS

* enter invalid 2FA code in the 2FA entry screen after logging in
* get returned back to login screen