Fix tests leaking readline history

[deivid-rodriguez]

Fixes @MSP-Greg's comment:

FYI, test times seem to be jumping around quite a bit. Seems that one of the test files is leaving artifacts that slow successive tests? As shown below:

2017-09-25_60014 464 runs, 527 assertions, 0 failures, 0 errors, 3 skips 132 sec
2017-10-01_60083 464 runs, 527 assertions, 0 failures, 0 errors, 3 skips 25 sec
2017-10-15_60184 464 runs, 527 assertions, 0 failures, 0 errors, 3 skips 144 sec
2017-11-01_60599 464 runs, 527 assertions, 0 failures, 0 errors, 3 skips 42 sec
2017-11-07_60677 464 runs, 527 assertions, 0 failures, 0 errors, 3 skips 112 sec
2017-11-09_60723 464 runs, 527 assertions, 0 failures, 0 errors, 3 skips 27 sec
2017-11-11_60742 464 runs, 527 assertions, 0 failures, 0 errors, 3 skips 89 sec
2017-11-13_60753 464 runs, 527 assertions, 0 failures, 0 errors, 3 skips 64 sec
2017-11-14_60760 464 runs, 527 assertions, 0 failures, 0 errors, 3 skips 33 sec
2017-11-14_60762 464 runs, 527 assertions, 0 failures, 0 errors, 3 skips 26 sec

2017-11-15_60767 BAD Stopped Byebug::ThreadTest
2017-12-09_61095_2 BAD Stopped Byebug::ThreadTest

[deivid-rodriguez]

@MSP-Greg Can you confirm this stabilizes test times for you?

[MSP-Greg]

@deivid-rodriguez

Yes, it does. Ran a few without logging info, they were all below 30 or so, then I decided to log them, shown below on the right is test time after the pr:

2017-09-25_60014   464 runs, 527 assertions, 0 failures, 0 errors, 3 skips  132 sec   32
2017-10-01_60083   464 runs, 527 assertions, 0 failures, 0 errors, 3 skips   25 sec
2017-10-15_60184   464 runs, 527 assertions, 0 failures, 0 errors, 3 skips  144 sec   22
2017-11-01_60599   464 runs, 527 assertions, 0 failures, 0 errors, 3 skips   42 sec
2017-11-07_60677   464 runs, 527 assertions, 0 failures, 0 errors, 3 skips  112 sec   15
2017-11-09_60723   464 runs, 527 assertions, 0 failures, 0 errors, 3 skips   27 sec
2017-11-11_60742   464 runs, 527 assertions, 0 failures, 0 errors, 3 skips   89 sec   17
2017-11-13_60753   464 runs, 527 assertions, 0 failures, 0 errors, 3 skips   64 sec   21
2017-11-14_60760   464 runs, 527 assertions, 0 failures, 0 errors, 3 skips   33 sec
2017-11-14_60762   464 runs, 527 assertions, 0 failures, 0 errors, 3 skips   26 sec   24

465 runs, 528 assertions, 0 failures, 0 errors, 3 skips  -- NEW result

[deivid-rodriguez]

Yay, much better! Thanks for testing and letting me know!