BuildCommand: the default result is an error

Summary:
The current logic and implementation may result that in SimpleConsole (with `-c ui.superconsole=DISABLED`) a failure may be reported as a success first and then as a true failure. This can happen because `BuildCommand`:
1. assumes SUCCESS as an initial status
2. doesn't handle all exceptions
3. issues a build finished `event` in the finally block `params.getBuckEventBus().post(BuildEvent.finished(started, exitCode));`

This change ensures that for `buck build` success will be reported only if it was a real success

Reviewed By: ttsugriy

fbshipit-source-id: 2c40ce9

src/com/facebook/buck/cli/BuildCommand.java

@@ -471,7 +471,7 @@ protected ExitCode run(
       this.arguments.addAll(additionalTargets);
     }
     BuildEvent.Started started = postBuildStartedEvent(params);
-    ExitCode exitCode = ExitCode.SUCCESS;
+    ExitCode exitCode = ExitCode.BUILD_ERROR;
     try (CloseableMemoizedSupplier<ForkJoinPool> poolSupplier =
         getForkJoinPoolSupplier(params.getBuckConfig())) {
       exitCode = executeBuildAndProcessResult(params, commandThreadManager, poolSupplier);