improve 'service' integration tests (#43655)

* service tests: check that daemon is really running

(spoiler: it isn't)

* service tests: add PIDFile directive in systemd unit

* service tests: check 'changed' too

* service tests: fix indentation & use changed test

* service tests: #16694 has been fixed a long time ago

* service tests: refactor

- always execute cleaning tasks
- move tests tasks in a dedicated file

* service tests: add test for #42786

* service tests: display value of ansible_service_mgr

* service tests: allow to run tests twice in a row

stop & disable ansible test service

* service tests: 'pattern' value must be a substring

'pattern' parameter is poorly named

* service tests: check ansible_test service status

* service tests: test daemon must handle SIGHUP

because 'initctl reload' sends SIGHUP, otherwise test daemon stops when
receiving the signal

* service tests: remove upstart override file too

and check that files were removed using raw module and stat command

test/integration/targets/service/files/ansible.systemd

@@ -5,6 +5,7 @@ Description=Ansible Test Service
 ExecStart=/usr/sbin/ansible_test_service "Test\nthat newlines in scripts\nwork"
 ExecReload=/bin/true
 Type=forking
+PIDFile=/var/run/ansible_test_service.pid
 
 [Install]
 WantedBy=multi-user.target