[Backport 2.2] Use correct base path to check if setup folder exists

[Jeroenll]

Original Pull Request

#20182

Description (*)

Current implementation checks the path base/data/web/magento2/pubsetup which is incorrect. It should be /data/web/magento2/pub/setup.

Fixed Issues (if relevant)

1. Web Setup Wizard not visible in backend magento 2.1.9 #11892
2. Web Setup Wizard not visible in backend (V.2.1.2) ONGOING #7623

Manual testing scenarios (*)

1. Install Magento and set doc root is pub/.
2. Symlink setup folder to pub.
3. Web Setup Wizard should be visible under System > Web Setup Wizard but it's not.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[m2-assistant]

Hi @JeroenVanLeusden. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me 2.2-develop instance - deploy vanilla Magento instance

For more details, please, review the Magento Contributor Assistant documentation

[Jeroenll]

@orlangur Can you also process this backport PR?

[orlangur]

@JeroenVanLeusden surely, I was already scared by an attempt in your personal fork)

[magento-engcom-team]

Hi @orlangur, thank you for the review.
ENGCOM-4768 has been created to process this Pull Request

[ghost]

@AlexWorking unfortunately, only members of the maintainers team are allowed to assign developers to the pull request

[ghost]

@AlexWorking unfortunately, only members of the maintainers team are allowed to assign developers to the pull request

[VasylShvorak]

✔️ QA passed

[m2-assistant]

Hi @JeroenVanLeusden, thank you for your contribution!
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