Attempt to stabilize MavenTargetDependencyEditorTest

Create more descriptive failure messages and delay validation of button
enablement to give the dialog more time to update.

org.eclipse.m2e.swtbot.tests/src/org/eclipse/m2e/pde/ui/MavenTargetDependencyEditorTest.java

@@ -234,8 +234,8 @@ public void testAddMavenLocation() throws Exception {
 		assertEquals(table.cell(19, 3), "");
 		assertEquals(table.cell(19, 4), "jar");
 
-		assertFalse(robot.button("Update").isEnabled());
-		assertFalse(robot.button("Finish").isEnabled());
+		assertFalse("Expected \"Update\" button to be disabled", robot.button("Update").isEnabled());
+		assertFalse("Expected \"Finish\" button to be disabled", robot.button("Finish").isEnabled());
 		// There is no elegant way to select the cell editor, but we
 		// know that it will be the first text widget in the dialog.
 		table.click(19, 0);
@@ -246,14 +246,14 @@ public void testAddMavenLocation() throws Exception {
 		robot.text(0).setText("3.12.0");
 		table.click(19, 3); // Close cell editor
 
-		assertTrue(robot.button("Update").isEnabled());
-		assertTrue(robot.button("Finish").isEnabled());
-
 		assertEquals(table.cell(19, 0), "org.apache.commons");
 		assertEquals(table.cell(19, 1), "commons-lang3");
 		assertEquals(table.cell(19, 2), "3.12.0");
 		assertEquals(table.cell(19, 3), "");
 		assertEquals(table.cell(19, 4), "jar");
+
+		assertTrue("Expected \"Update\" button to be enabled", robot.button("Update").isEnabled());
+		assertTrue("Expected \"Finished\" button to be enabled", robot.button("Finish").isEnabled());
 	}
 
 	/**