Support PHP-FPM in command.php

[nathanjosiah]

Remove assumption that PHP_BINARY will always be acceptable.

Description

command.php assumes that if PHP_BINARY is set that it is always the PHP cli bin. When FPM is used, the bin will be php-fpm which isn't compatible with the PHP cli. This PR removes that constant and instead uses the already present PHP_BINDIR usage

Fixed Issues (if relevant)

1. command.php assumes that PHP_BINARY is always the PHP cli binary #216: command.php assumes that PHP_BINARY is always the PHP cli binary

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/verification tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)
• Changes to Framework doesn't have backward incompatible changes for tests or have related Pull Request with fixes to tests

[magento-cicd2]

All committers have signed the CLA.

[coveralls]

Coverage remained the same at 57.092% when pulling 4328833 on magento-trigger:fpm-compatibility into e187c33 on magento:develop.

[KevinBKozan]

@nathanjosiah Thank you for your contribution! We will update this PR with progress information as we process it.

[KevinBKozan]

Changes look good, I can confirm that this command.php change does not affect non-valet setups.