After a write operation on an index, a post-operation global checkpoint
sync fires. Previously, this action fired on the same user as executed
the write action. If the user did not have priviledges for this action,
the global checkpoint sync would fail. With an upstream change in core,
this action now fires as the system user. This commit adds a test that
create a user that has minimal write permissions on an index, but none
that would imply it could execute the global checkpoint sync. This then
serves as a test that the upstream change to fire the global checkpoint
sync as the system user is correct. This test must run as a mulit-node
test so that a replica is a assigned so that the global checkpoint sync
fires in the first place. This test does indeed fail without the
upstream change, and passes with it.
Relates elastic/x-pack-elasticsearch#2744
Original commit: elastic/x-pack-elasticsearch@bf7e771756
Jason Tedor