Remove php7 beta feature, move logged-in users to use the extracted cookie as well.
 Allow directing a percentage traffic to the api cluster to php7 at the varnish layer
 Use php7 to run maintenance scripts
 Ramp up percentage of users on php7.2 to 100% on both API and appserver clusters
 Use php7 for processing async jobs (stretch)
 Remove hhvm from production (stretch)