Bug 54406: Speed up Parsoid job processing

Parsoid jobs were not dequeued fast enough to keep up during heavy editing.
The API load has been hovering around 30%, which leaves some room for higher
Parsoid dequeue rates.

This patch doubles the peak dequeue rate for Parsoid jobs. This will increase
the load on the API cluster by at most ~10%, likely closer to 5%. We'll
monitor the load on deployment.

Change-Id: I1a9aa38b2ef7f1eac6bba9c516690b2b1452a276
Merge "Bug 54406: Speed up Parsoid job processing" into production