[1.0.2] test-packages should just ignore packages without tests and not fail

[mcbain]

Before 1.0.2 it was possible to test all packages by simply run:

meteor test-packages packages/*

With 1.0.2 one have to add a dummy test or to select all package with tests to prevent.

While trying to test package `packages/xxx`:
error: Package has no tests

[mcbain]

It sufficient to add empty onTest block.

 Package.onTest(function (api) {});

[glasser]

Yes, I think you're right.