Summary:
It is not the first time panoptic instant test fails with memory error:

https://our.intern.facebook.com/intern/fblearner/details/166744913/operator/1735305631/

increasing the memory requirement might fix it.

Reviewed By: rbgirshick

Differential Revision: D19782277

fbshipit-source-id: 9beca005f807c12c5b35cf3e1a3174701e592b10