Running a test can block the dashboard until the page timesout or the test finishes

[josebolos]

When a new URL is added to the Dashboard and you click on the "Run test" or the "Click here to generate new results" links, Dashboard won't show a response until the test has finished running, either because it has completed successfully, or the test timed out.

It can be reproduced by adding a page known to be very slow (e.g. https://www.reddit.com/). It may be related to #288 as the symptoms can be similar, even if this is happening even with Node.js v8.