Perform atomic test cleanup of multiple projects eclipse-platform#275

The UIEditWorkingSetWizardAuto#testEditPage randomly fails because the
project deletion during test cleanup fails. The project file of the
second project to be deleted is already locked.

To avoid that the deletion of the first project triggers some
asynchronous tasks that interfere with the deletion of the second
project, this change combines both deletions into an atomic workspace
operation. In addition, the change separates the exception handling for
both projects to see from the stack trace which of the deletions caused
the exception.

Contributes to
eclipse-platform#275

tests/org.eclipse.ui.tests/Eclipse UI Tests/org/eclipse/ui/tests/dialogs/UIWorkingSetWizardsAuto.java

@@ -18,6 +18,7 @@
 
 import org.eclipse.core.resources.IFile;
 import org.eclipse.core.resources.IProject;
+import org.eclipse.core.resources.ResourcesPlugin;
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.IStatus;
 import org.eclipse.jface.wizard.IWizard;
@@ -89,20 +90,20 @@ protected void checkTreeItems() {
 		}
 	}
 
-	private void deleteResources() {
-		try {
-			if (p1 != null) {
-				FileUtil.deleteProject(p1);
-			}
-			if (p2 != null) {
-				FileUtil.deleteProject(p2);
-			}
+	private void deleteResources() throws CoreException {
+		ResourcesPlugin.getWorkspace().run(__ -> {
+			deleteProject(p1);
+			deleteProject(p2);
+		}, null);
+	}
 
+	private void deleteProject(IProject project) {
+		try {
+			FileUtil.deleteProject(project);
 		} catch (CoreException e) {
 			TestPlugin.getDefault().getLog().log(e.getStatus());
 			throw createAssertionError(e);
 		}
-
 	}
 
 	private AssertionError createAssertionError(CoreException originalException) {