Add support for the external auth domain user attribute

[jvlcek]

https://bugzilla.redhat.com/show_bug.cgi?id=1424618

This PR is paired with PR 15535 in the ManageIQ/manageiq repo. Both must be merged at the same time.

Note:

This change requires new support in the underlying SSSD code. Updates were
required to provide the domain name when MiQ is configured to use External Authentication (Mode: External (httpd)

The BZs that track this work are:

BZ 1425891
BZ 1455254
The fixes for these BZs are targeted for RHEL 7.4 GA and CentOS 7.4

Therefor this change should not be merged until MiQ appliance builds migrate to RHEL 7.4 GA and CentOS 7.4

Testing:

• With the associated PR in place use the appliance console to configure: Configure External Authentication (httpd)
• Configure the appliance for external authentication
• Add a valid group
• login with a valid user
• confirm the user record has a userid in User Principal Name format

[jvlcek]

@gtanzillo and @abellotti please review.

I have tested this change on a live appliance configured with the associated PRs.

• manageiq 15535
• manageiq-appliance 127

[miq-bot]

Checked commit jvlcek@9ccbb45 with ruby 2.2.6, rubocop 0.47.1, and haml-lint 0.20.0
1 file checked, 0 offenses detected
Everything looks fine. 👍

[gtanzillo]

👍

[simaishi]

Fine backport details:

$ git log -1
commit bd6144de033033d827b1c7c85be40cf2fef4bddb
Author: Gregg Tanzillo <[email protected]>
Date:   Thu Aug 31 18:19:29 2017 -0400

    Merge pull request #250 from jvlcek/bz1424618_dup_users
    
    Add support for the external auth domain user attribute
    (cherry picked from commit a8955426ccd2492a51934a3f7bfe45b291072a38)
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1487689