PerformanceTest should inherit default configuration

We need to refactor it - DRY.

In `package.scala` in the core module:

    def withTestContext[U](ctx: Context, log: Log, handler: Events)(body: =>U) {
      for {
        _ <- dyn.log.using(log)
        _ <- dyn.events.using(handler)
        _ <- dyn.currentContext.using(ctx)
      } body
    }

In `PerformanceTest.main`:

    val ctx = dyn.currentContext.value ++ Main.Configuration.fromCommandLineArgs(args).context
    withTestContext(ctx, Log.Console, Events.None) {
      // ...
    }

In `ScalameterFramework`, also `withTestContext` instead of for-comprehensions.