Snapshot fails in "only" mode, but not with a full test run

[Torben Ewert]

When some JavaScript is initializing the tested component, (for example with a slider) it makes a difference, if OSnap runs only the tested component, or if it is running all tests.

I think this has to do with the parallelism and the time it takes to initialize the JavaScript.
When all tests are run, the page has more time to load, because there are potentially more workers spawned.
Setting a "timeout" action doesn't prevent the problem though.

I will have to investigate this. With this issue present, something like #10 would not work reliably...