This commit reverts a previous change where searcher were not wrapped when the RequestContext
could not be found. If DLS/FLS is enabled, which is the default, any bulk request that contains an
update request will not be permitted. This change also exposes the ability to completely disable DLS
and FLS so that users who are not using these features can still use bulk updates.
See elastic/elasticsearch#938
Original commit: elastic/x-pack-elasticsearch@513782db1c