Fix tests to not use --exit flag for more graceful termination

[ntgomes]

According to https://stackoverflow.com/a/46759250, using the --exit flag for mocha is not advised since it's only hiding the true issue of unclosed connections that chai-mocha is waiting for after all tests pass. Find what unclosed connection there is that's blocking mocha from terminating without the --exit flag, and make changes to close that connection properly.

[ntgomes]

Update: according to chai-http developers, having --exit is fine due to change in default behavior. chaijs/chai-http#178 (comment)

So the guy from the StackOverflow answer probably didn't understand what they were talking about.