Wait for FAMILY_SNAPSHOT jobs after creating projects/teardown

org.eclipse.core.internal.resources.DelayedSnapshotJob.run(IProgressMonitor)
is triggered both periodically and on few special cases. Special cases
are project deletion and creation, options change...

This job may create change events coming to JDT from non-UI thread, see
org.eclipse.jdt.internal.core.DeltaProcessor.resourceChanged(IResourceChangeEvent).

To avoid sporadic test fails we should also wait for that job.

Note: we can't unconditionally call waitForSnapShot(), it should be
always done outside of the code that holds workspace rule, otherwise we
will run in deadlocks with other jobs...

See #2716

org.eclipse.jdt.core.tests.model/src/org/eclipse/jdt/core/tests/model/AbstractJavaModelTests.java

@@ -4107,6 +4107,7 @@ public void waitForManualRefresh() {
 			try {
 				Job.getJobManager().wakeUp(ResourcesPlugin.FAMILY_MANUAL_REFRESH);
 				Job.getJobManager().join(ResourcesPlugin.FAMILY_MANUAL_REFRESH, null);
+				waitForSnapShot();
 				JavaModelManager.getIndexManager().waitForIndex(isIndexDisabledForTest(), null);
 				wasInterrupted = false;
 			} catch (OperationCanceledException e) {
@@ -4127,6 +4128,27 @@ public static boolean isTouchJobRunning() {
 		return false;
 	}
 
+	public void waitForSnapShot() {
+		if (isWorkspaceRuleAlreadyInUse(getWorkspaceRoot())){
+			// Don't wait holding workspace lock on FAMILY_SNAPSHOT, because
+			// we might deadlock with DelayedSnapshotJob
+			System.out.println("\n\nAborted waitForSnapShot() because running with the workspace rule\n\n");
+			return;
+		}
+		boolean wasInterrupted = false;
+		do {
+			try {
+				Job.getJobManager().wakeUp(ResourcesPlugin.FAMILY_SNAPSHOT);
+				Job.getJobManager().join(ResourcesPlugin.FAMILY_SNAPSHOT, null);
+				wasInterrupted = false;
+			} catch (OperationCanceledException e) {
+				e.printStackTrace();
+			} catch (InterruptedException e) {
+				wasInterrupted = true;
+			}
+		} while (wasInterrupted);
+	}
+
 	public void waitUntilIndexesReady() {
 		// dummy query for waiting until the indexes are ready
 		SearchEngine engine = new SearchEngine();