Make IT port number configurable

The PerformanceAnalyzerIT class previously assumed that the Performance
Analyzer Webservice would always be listening on port 9600 for any
deployment of PerformanceAnalyzer.

Since this isn't always the case, this commit makes the port number
configurable through a gradle property.

gradle.properties

@@ -8,8 +8,11 @@ systemProp.tests.rest.cluster=localhost:9200
 # The Elasticsearch cluster node communication endpoint
 systemProp.tests.cluster=localhost:9300
 
-# Comment this in if you want a cluster spun up for integration testing
+# Set this to true if you want a cluster spun up for integration testing
 systemProp.tests.useDockerCluster=false
 
-# Comment this in to enable integration testing
+# Set this to true if you want to enable integration testing
 systemProp.tests.enableIT=false
+
+# The port number for the PerformanceAnalyzer WebService
+systemProp.tests.pa.port=9600

src/test/java/com/amazon/opendistro/elasticsearch/performanceanalyzer/PerformanceAnalyzerIT.java

@@ -28,7 +28,7 @@
 
 public class PerformanceAnalyzerIT extends ESRestTestCase {
     private static final Logger LOG = LogManager.getLogger(PerformanceAnalyzerIT.class);
-    private static final int PORT = 9600;
+    private static final int PORT = Integer.parseInt(System.getProperty("tests.pa.port"));
     private static final ObjectMapper mapper = new ObjectMapper();
     private static RestClient paClient;