collect console log in renderer tests

[aminya]

This is a patch for #50 that collects the console log and prints it at the end.

[aminya]

@DeeDeeG turns out using async.parallel does not work well with Atom. Switching to async.series, now most of the tests pass without any issues.

We can try async.parallelLimit with which limits the number of processes that run in parallel. Setting the number to 2 may be enough for letting another process to run in case of a timeout.