Stop environment (#4283)

* Use docker-compose down to remove networks

Docker-compose creates a unique network for each build now. docker-compose rm -v -f did not remove the created networks. The command `docker-compose down` does also remove the networks.

This is important as docker-compose has a default limit of 31 networks.

* Stop environment is now call as part of the testsuite

The testsuite command cleans up the environment after being finished. This reduces the number of containers run at the same time on the machine and saves resources. So far cleanup only happend after all testsuites for all beats were executed.

The cleanup afterwards is still needed, as cleanup will not happen in case a test fails.

libbeat/scripts/Makefile

@@ -239,6 +239,10 @@ testsuite: clean update
 	$(MAKE) benchmark-tests
 	$(MAKE) coverage-report
 
+	if [ $(TEST_ENVIRONMENT) = true ]; then \
+		$(MAKE) stop-environment; \
+    fi
+
 # Generates a coverage report from the existing coverage files
 .PHONY: coverage-report
 coverage-report: