Fix parallel MQTT itests execution (#8617)

* Improve exception handling of the embedded MQTT broker so the port can be reconfigured when it is already bound and it properly unlocks files
* Rework MQTT integration tests so they each run the embedded broker on their own reserved port

Signed-off-by: Wouter Born <github@maindrain.net>

itests/org.openhab.binding.mqtt.homeassistant.tests/pom.xml

@@ -100,4 +100,27 @@
     </dependency>
   </dependencies>
 
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.codehaus.mojo</groupId>
+        <artifactId>build-helper-maven-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>reserve-network-port</id>
+            <goals>
+              <goal>reserve-network-port</goal>
+            </goals>
+            <phase>process-resources</phase>
+            <configuration>
+              <portNames>
+                <portName>mqttembeddedbroker.port</portName>
+              </portNames>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+
 </project>