adding null search shard for log silence

this is a rewrite of https://gerrit.wikimedia.org/r/#/c/52547/2
which ram wrote, but rebasing was not coming easily, so I just
wrote a new patchset

Change-Id: Ie95c58fe0532c9a5c8790b26037b64137c2f5a2e
Use latest php

Use the latest PHP package, so that upgrades can be done via dsh

Change-Id: I48d95b2f9fe281d837f35ca5b75d51fd5a00f7fd
Merge "adding null search shard for log silence" into production