Fix recurring test failure in PlatformUITest#testCreateAndRunWorkbench #1517

The RCPTestWorkbenchAdvisor uses static fields to track the state of
startup operations. These fields were not reset between test runs.
If PlatformUITest.testCreateAndRunWorkbench is run multiple times
(e.g. in a suite or during repeated test execution), the 'started'
flag would remain 'true' from the previous run, causing assertions
in subsequent runs to fail (as operations would incorrectly report
running after startup).

This change resets 'started' and the result flags to their initial
state in preStartup().

Author: vogella

tests/org.eclipse.ui.tests.harness/src/org/eclipse/ui/tests/harness/util/RCPTestWorkbenchAdvisor.java

@@ -127,6 +127,15 @@ public void eventLoopIdle(final Display display) {
 
 	@Override
 	public void preStartup() {
+		synchronized (RCPTestWorkbenchAdvisor.class) {
+			started = false;
+		}
+		asyncDuringStartup = null;
+		syncWithDisplayAccess = null;
+		asyncWithDisplayAccess = null;
+		syncWithoutDisplayAccess = null;
+		asyncWithoutDisplayAccess = null;
+
 		super.preStartup();
 		final Display display = Display.getCurrent();