The .security index used several different types to differentiate the
documents added to the index (users, reserved-users, roles, etc). Since
types are deprecated in 6.x, this commit changes the .security index
access layer to only use a single type and have all documents in the
index be of that single type. To differentiate documents that may have
the same id (e.g. the same user name and role name), the appropriate
type of the document is prepended to the id. For example, a user named
"jdoe" will now have the document id "user-jdoe".
This commit also ensures that any native realm security index operations
that lead to auto creation of the security index first go through the process
of creating the internal security index (.security-v6) and creating the alias
.security to point to the internal index.
Lastly, anytime the security index is accessed without having been
upgraded, an exception is thrown notifying the user to use the
upgrade API to upgrade the security index.
Original commit: elastic/x-pack-elasticsearch@cc0a474aed
a68fb27a23