Fetch Cart: integration tests for catalog product image endpoint

[garmashdev]

Description

Added integration tests for new API endpoint : "/V1/bolt/boltpay/product/:productId/image-url"

Fixes: https://app.asana.com/0/1201931884901947/1203149984454994/f

#changelog integration tests for "/V1/bolt/boltpay/product/:productId/image-url"

Type of change

• [ ] Bug fix (change which fixes an issue)
• [ ] New feature (change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How Has This Been Tested?

Please validate that you have tested your change in at least one of the following areas:

• [ ] Successfully tested locally (or docker image)
• [ ] Successfully tested on a staging or sandbox server
• [ ] Successfully tested on a merchant's staging server

For PR Reviewer

• [ ] Reviewed unit tests to make sure we are using real components rather than mocks as much as possible?
• [ ] For any major change (observer, new Bolt feature, core Magento interaction) we must add a feature switch, did you verify this?

Checklist:

• [ ] My code follows the style guidelines of this project.
• [ ] I have performed a self-review of my own code.
• [ ] I have commented my code, particularly in hard-to-understand areas.
• [ ] New and existing unit tests pass locally with my changes.
• [ ] I have created or modified unit tests to sufficiently cover my changes.
• [ ] I have added my ticket link and provided a changelog message.

[danac-gs]

@vitaliyreznikov @dumega Should PHP7.1 & Magento2.2 tests be removed?