Add some selfupdate integration tests #570

Job	Run time
CI test (make validate)	30s
Code coverage (codecov)	0s
SelfUpdate tests (PHAR) (8.2)	21s
SelfUpdate tests (PHAR) (8.1)	24s
SelfUpdate tests (PHAR) (8.0)	20s
SelfUpdate tests (PHAR) (7.4)	8s
Build moodle-plugin-ci.phar	33s
Integration tests (8.2, master)	5m 18s
Integration tests (8.2, MOODLE_403_STABLE)	5m 13s
Integration tests (8.2, MOODLE_402_STABLE)	5m 14s
Integration tests (8.1, MOODLE_401_STABLE)	5m 54s
Integration tests (8.0, MOODLE_400_STABLE)	6m 58s
Integration tests (8.0, MOODLE_311_STABLE)	5m 10s
Integration tests (7.4, MOODLE_310_STABLE)	5m 15s
Integration tests (7.4, MOODLE_39_STABLE)	5m 5s
Integration tests (7.4, MOODLE_38_STABLE)	5m 16s
Integration tests (PHAR) (8.2, master)	5m 0s
Integration tests (PHAR) (8.1, MOODLE_403_STABLE)	4m 48s
Integration tests (PHAR) (8.0, MOODLE_401_STABLE)	5m 39s
Integration tests (PHAR) (7.4, MOODLE_400_STABLE)	5m 6s
	1h 12m 12s

Provide feedback