feat: add port as a parameter for the bigtable emulator

Author: andre-sampaio

google-cloud-bigtable-emulator-core/src/main/java/com/google/cloud/bigtable/emulator/core/EmulatorController.java

@@ -93,12 +93,13 @@ public synchronized boolean isRunning() {
   }
 
   /** Starts the emulator process and waits for it to be ready. */
-  public synchronized void start() throws IOException, TimeoutException, InterruptedException {
+  public synchronized void start(int port) throws IOException, TimeoutException, InterruptedException {
     if (!isStopped) {
       throw new IllegalStateException("Emulator is already started");
     }
-    this.port = getAvailablePort();
-
+    
+    this.port = port;
+    
     // Try to align the localhost address across java & golang emulator
     // This should fix issues on systems that default to ipv4 but the jvm is started with
     // -Djava.net.preferIPv6Addresses=true
@@ -143,6 +144,11 @@ public synchronized void start() throws IOException, TimeoutException, Interrupt
     waitForPort(port);
   }
 
+  /** Starts the emulator process and waits for it to be ready. */
+  public synchronized void start() throws IOException, TimeoutException, InterruptedException {
+    start(getAvailablePort());
+  }
+
   /** Stops the emulator process. */
   public synchronized void stop() {
     if (isStopped) {