Use the new repmgr preload library name

[carbonin]

See: ManageIQ/manageiq-appliance#201

[miq-bot]

Checked commit carbonin@78cf80e with ruby 2.3.3, rubocop 0.52.1, haml-lint 0.20.0, and yamllint 1.10.0
1 file checked, 1 offense detected

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• 💣 💥 🔥 🚒 - Linter/Yaml - missing config files

[simaishi]

Hammer backport details:

$ git log -1
commit 21e35fd3be713e185bcc59054152faea553985a9
Author: Brandon Dunne <brandondunne@hotmail.com>
Date:   Tue Aug 14 09:57:49 2018 -0400

    Merge pull request #300 from carbonin/use_new_repmgr_preload_lib
    
    Use the new repmgr preload library name
    (cherry picked from commit c7f269fe2542aaaccc72da891ed074915d29e77e)