make cache purge environment aware

[jafowler]

This PR aims to make the zone cache functions environment aware. As of right now, the plan is to allow users to include zone versioning environments when they call their cache purge functions.

php vendor/bin/phpunit --configuration phpunit.xml
PHPUnit 5.7.27 by Sebastian Bergmann and contributors.

...............................................................  63 / 158 ( 39%)
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Time: 4.8 seconds, Memory: 8.00MB

OK (158 tests, 983 assertions)

[mgirouard]

lgtm