Error stacks from `runFilenameOrFn` are pretty useless

[juliemr]

The stack that gets appended to a bad onprepare or onshutdown script from https://github.com/angular/protractor/blob/master/lib/util.ts#L57 is pretty useless, since it's always the same and is asynchronous so it doesn't point to the right file. We could maybe just use an empty string?

[sjelin]

We could also grab the stack trace at the top of the function and stick that in too