Haystack attempts to always ensure the index mapping is up-to-date.
There is a bug in this code (at least when using Elasticsearch 1.x) that
results in an invalid mapping comparison. Given that our mapping is
static, this feature is simply a waste of resources since we always
make three API calls to Elasticsearch for every search call.

This commit disables this mapping check/update feature when executing a
search query.

LEARNER-2188