This change allows reads of our native users and roles when the template version has not been updated to
match the current version. This is useful for rolling upgrades where the nodes are also being actively
queried and/or indexed into. Without this, we can wreak havoc on a cluster by causing exceptions during
replication, which leads to shard failures. On nodes that match the version defined in the template,
write operations are allowed since we know that we are backwards compatible in terms of format but we
may have added new fields and shouldn't index them until the mappings and template have been updated.
As part of this, the rolling upgrade tests from core were used as the basis for a very basic set of tests
for doing a rolling upgrade with x-pack.
Closeselastic/elasticsearch#4126
Original commit: elastic/x-pack-elasticsearch@9be518ef00
4239ba5415