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.homie.tests/itest.bndrun

@@ -13,6 +13,10 @@ Fragment-Host: org.openhab.binding.mqtt.homie
 -runblacklist: \
 	bnd.identity;id='org.openhab.core.storage.json'
 
+-runvm: \
+	-Dio.netty.noUnsafe=true,\
+	-Dmqttembeddedbroker.port=${mqttembeddedbroker.port}
+
 #
 # done
 #
@@ -89,4 +93,4 @@ Fragment-Host: org.openhab.binding.mqtt.homie
 	org.opentest4j;version='[1.2.0,1.2.1)',\
 	org.reactivestreams.reactive-streams;version='[1.0.2,1.0.3)',\
 	moquette-broker;version='[0.13.0,0.13.1)'
--runvm: -Dio.netty.noUnsafe=true
+