Reworked multi-tenancy support for new Kibana 7.12 index naming scheme

...ain/java/com/floragunn/searchguard/SearchGuardPlugin.java

...floragunn/searchguard/privileges/PrivilegesEvaluator.java

...oragunn/searchguard/privileges/PrivilegesInterceptor.java

...a/com/floragunn/searchguard/support/ReflectionHelper.java

.../java/com/floragunn/searchguard/HttpIntegrationTests.java

.../searchguard/configuration/PrivilegesInterceptorImpl.java

...unn/searchguard/test/helper/cluster/EsClientProvider.java

...agunn/searchguard/test/helper/rest/GenericRestClient.java