This change addresses some issues regarding thread safety around
updates and method calls on the XPackLicenseState object. There exists
a possibility that there could be a concurrent update to the
XPackLicenseState when there is a scheduled check to see if the license
is expired and a cluster state update. In order to address this, the
update method now has a synchronized block where member variables are
updated. Each method that reads these variables is now also
synchronized.
Along with the above change, there was a consistency issue around
security calls to the license state. The majority of security checks
make two calls to the license state, which could result in incorrect
behavior due to the checks being made against different license states.
The majority of this behavior was introduced for 6.3 with the inclusion
of x-pack in the default distribution. In order to resolve the majority
of these cases, the `isSecurityEnabled` method is no longer public and
the logic is also included in individual methods about security such as
`isAuthAllowed`. There were a few cases where this did not remove
multiple calls on the license state, so a new method has been added
which creates a copy of the current license state that will not change.
Callers can use this copy of the license state to make decisions based
on a consistent view of the license state.
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