Reload ApplicationSetting column information before use

What does this MR do?

It seemed check_namespace_plan? column is not detected in migration. This happens when all migrations are run from scratch. One possible cause is that ApplicationSetting is used prior to 20170512173638, thus the column in memory does not contain check_namespace_plan?.

This has been the behavior for Rails https://github.com/rails/rails/issues/6939

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/quality/nightly/issues/74

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• EE specific content should be in the top level /ee folder
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• Security reports checked/validated by reviewer