gplazma-fermi: fix last modified check in junit test

Motivation:

The current code (givenFileUpdated())does not guarantee that
the file's mtime value actually changes, resulting occasionally
in junit test case failure.

Modification:

Use a wait/sleep loop to check the value of the mtime and
exit when it is different.

Result:

Should no longer encounter this test case failure.

Target: master
Request: 4.1
Request: 4.0
Request: 3.2
Request: 3.1
Request: 3.0
Request: 2.16
Acked-by: Paul
Acked-by: Dmitry

modules/gplazma2-fermi/src/test/java/org/dcache/gplazma/plugins/VOGroupPluginTest.java

@@ -68,6 +68,7 @@ LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 import java.util.HashSet;
 import java.util.Optional;
 import java.util.Set;
+import java.util.concurrent.TimeUnit;
 
 import org.dcache.auth.FQANPrincipal;
 import org.dcache.auth.GidPrincipal;
@@ -89,6 +90,7 @@ public class VOGroupPluginTest {
     public void setUp() throws Exception {
         URL url = ClassLoader.getSystemResource(TEST_FIXTURE);
         file = new File(url.toURI());
+        file.setLastModified(System.currentTimeMillis() - TimeUnit.DAYS.toMillis(1));
         map = new FileBackedVOGroupMap(file.getAbsolutePath());
         plugin = new VOGroupPlugin(map);
     }