Fix Drush5 error - Pantheon hosted Developer Portals

[trevorcarr-1]

This applies to sites hosted on Pantheon that have recently upgraded to the latest Apigee release.

When no Drush version is specified within the pantheon.yml file, some sites are defaulting to Drush5 rather than Drush8. The error in question:

The error log shows the following:

PHP Fatal error: Uncaught Error: Call to undefined function 
mysql_connect() in /etc/drush/drush-5-extensions/pantheon.drush.inc:127 
Stack trace: 
#0 /opt/pantheon/drush5/includes/command.inc(334): drush_pantheon_is_drupal_installed() 
#1 /opt/pantheon/drush5/includes/command.inc(208): _drush_invoke_hooks('is_drupal_insta...', Array, 'pantheon') 
#2 /opt/pantheon/drush5/includes/command.inc(175): drush_command() 
#3 /opt/pantheon/drush5/drush.php(92): drush_dispatch(Array) 
#4 /opt/pantheon/drush5/drush.php(61): _drush_bootstrap_and_dispatch() 
#5 /opt/pantheon/drush5/drush.php(16): drush_main() 
#6 {main} 
thrown in /etc/drush/drush-5-extensions/pantheon.drush.inc on line 12

To fix the error, simply define this value `drush_version: 8` in the pantheon.yml file.