[test] Some cases in DownloadService2Test are unstable with jre9-b96

If we run them one by one, they will pass. But when we run the whole suite, some cases will fail
Affected tests:
RULE DownloadService2Test::testGetCachedResourceNullVersion any any
RULE DownloadService2Test::testGetCachedResource_AllVersions any any
RULE DownloadService2Test::testGetCachedResource_AllVersions2 any any
RULE DownloadService2Test::testGetCachedResource_ExtraFS any any
RULE DownloadService2Test::testGetCachedResource_JAR any any
RULE DownloadService2Test::testGetUpdateAvailableEmptyVersion_Negative any any
RULE DownloadService2Test::testGetUpdateAvailableNullVersion any any
RULE DownloadService2Test::testGetUpdateAvailable_APP any any
RULE DownloadService2Test::testGetUpdateAvailable_APPLET any any
RULE DownloadService2Test::testGetUpdateAvailable_JAR any any
RULE DownloadService2Test::testGetUpdateAvailable_JARV1 any any