Support logins when "Get User Groups from LDAP" is not checked

[jvlcek]

When not getting groups from LDAP the user is manually created in
the DB. The name must be created in the format supported by the
directory being used. When the directory is Active Directory the username
must be in UPN format. When the directory is LDAP the username must be the
full DN. The admin will create the user in the UPN or DN formats as return from
searching the given directory.

https://bugzilla.redhat.com/show_bug.cgi?id=1442791

Steps for Testing/QA

1. Configure MiQ authentication with mode LDAP(S)
2. Do not select Get User Groups from LDAP
3. Ensure Base DN and Bind DN had not been filled in.
4. Manually create a test user with a simple username, must be the full DN or UPN e.g. adtestuser@example.com or cn=ldaptestuser,ou=people,ou=prod,dc=example,dc=com, and assign the user a group.
5. Confirm attempts to log in with the test user succeed.

[jvlcek]

@gtanzillo and @abellotti please review.

[jvlcek]

@miq-bot add_label authentication, bug

[jvlcek]

After configuring authentication to not Get User Groups from LDAP and manually creating users, if the authentication configuration is update to Get User Groups from LDAP duplicate user records could be created. I think we can manage this unlikely side effect by documenting it.
MattP, of QE, agreed that documenting this side effect for this unlikely scenario would be acceptable.

[miq-bot]

Checked commits jvlcek/manageiq@c045aff~...0119cda with ruby 2.2.6, rubocop 0.47.1, and haml-lint 0.20.0
3 files checked, 0 offenses detected
Everything looks fine. ⭐

[jvlcek]

@abellotti and @gtanzillo Updates made as discussed. If you are good with this let me know and I will squash the extra commits.

[gtanzillo]

👍 LGTM