* Restrict which tasks can use testclusters
This PR fixes a problem between the interaction of test-clusters and
build cache.
Before this any task could have used a cluster without tracking it as
input.
With this change a new interface is introduced to track the tasks that
can use clusters and we do consider the cluster as input for all of
them.
Test clusters currently has its own set of logic for dealing with
finding different versions of Elasticsearch, downloading them, and
extracting them. This commit converts testclusters to use the
DistributionDownloadPlugin.
* TestClusters: Convert the security plugin
This PR moves security tests to use TestClusters.
The TLS test required support in testclusters itself, so the correct
wait condition is configgured based on the cluster settings.
* PR review
This performs a simple restart test to move a basic licensed
cluster from no security (the default) to security & transport TLS
enabled.
Backport of: #41933
Alpar Torok
Ryan Ernst
Mark Vieira
Tim Vernum