Fix for #12969 - server port detection for errors

[lstellway]

Description

Updates getHostUrl() method to reference HTTP_HOST rather than SERVER_PORT.

Fixed Issues

1. magento/magento2#12969 - processor.php getHostUrl() does not detect the server port correctly

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)

[magento-cicd2]

All committers have signed the CLA.

[josefbehr]

@loganstellway Thank you for your contribution. Can you please fix the failing static tests?

FILE: /home/travis/build/magento/magento2/pub/errors/processor.php

FOUND 2 ERRORS AFFECTING 2 LINES

382 | ERROR | [x] Missing short description
383 | ERROR | [x] There must be exactly one blank line before tags

[magento-engcom-team]

Hi @josefbehr, thank you for the review.
ENGCOM-3160 has been created to process this Pull Request

[magento-engcom-team]

@loganstellway thank you for contributing. Please accept Community Contributors team invitation here to gain extended permissions for this repository.

[magento-engcom-team]

Hi @loganstellway. Thank you for your contribution.
We will aim to release these changes as part of 2.3.1.
Please check the release notes for final confirmation.