JDK9 removed pathname canonicalization when constructing FilePermission objects, which breaks some of the FilePermissions added by
Elasticsearch. This commit adds the system property jdk.io.permissionsUseCanonicalPath which makes JDK9 behave like JDK8 w.r.t. FilePermissions (see
https://github.com/elastic/elasticsearch/issues/21534).
As discussed at https://github.com/elastic/elasticsearch-cloud-azure/issues/91#issuecomment-229113595, we know that the current `discovery-azure` plugin only works with Azure Classic VMs / Services (which is somehow Legacy now).
The proposal here is to rename `discovery-azure` to `discovery-azure-classic` in case some users are using it.
And deprecate it for 5.0.
Closes#19144.