Log and continue if cache directory is not available
Log and continue if cache directory is not available

Instead of silently crashing the extension when Redis has been configured as a cache.

Magento documentation suggests the cache directory should exist even in this circumstance but experience has demonstrated otherwise. http://devdocs.magento.com/guides/v2.0/howdoi/php/php_clear-dirs.html
section-io/magento-metrics,section-io/magento-metrics