Fix key_pair class lookup

[kbrock]

The issue: it was not able to detect the correct provider specific class for AuthKeyPair

While we would like to avoid delegation, easier to just point to
the parent manager for auth key pairs

fixes issue with #19473
related to https://bugzilla.redhat.com/show_bug.cgi?id=1767747

irb(main):002:0> MiqExpression.miq_adv_search_lists('CloudNetwork', :exp_available_finds)
PostgreSQLAdapter#log_after_checkout, connection_pool: size: 30, connections: 1, in use: 1, waiting_in_queue: 0
Traceback (most recent call last):
       12: from lib/miq_expression.rb:903:in `miq_adv_search_lists'
       11: from lib/miq_expression.rb:802:in `model_details'
       10: from lib/miq_expression.rb:891:in `get_relats'
        9: from lib/miq_expression.rb:942:in `build_relats'
        8: from lib/miq_expression.rb:942:in `each'
        7: from lib/miq_expression.rb:973:in `block in build_relats'
        6: from lib/miq_expression.rb:942:in `build_relats'
        5: from lib/miq_expression.rb:942:in `each'
        4: from lib/miq_expression.rb:952:in `block in build_relats'
NameError (uninitialized constant ManageIQ::Providers::NetworkManager::AuthKeyPair)

[miq-bot]

Checked commit kbrock@fe2e292 with ruby 2.4.6, rubocop 0.69.0, haml-lint 0.20.0, and yamllint 1.10.0
1 file checked, 0 offenses detected
Everything looks fine. 🍰

[djberg96]

👍

[simaishi]

Ivanchuk backport details:

$ git log -1
commit cb6f2fb2c32a53651adf6b2c5020c2d5837a668d
Author: Jason Frey <[email protected]>
Date:   Fri Nov 8 12:21:21 2019 -0500

    Merge pull request #19486 from kbrock/manager_delegate_fixup

    Fix key_pair class lookup

    (cherry picked from commit 4640261fa9b0acc0eee2084785e5d0570578be86)

    https://bugzilla.redhat.com/show_bug.cgi?id=1785374