Exit with a non-zero status in check_tests script

[ghost]

Both scripts check_test and check_cronjob_test are used when running
Travis CI, and it was observed that the CI was still passing if any of
the commands in the scripts failed.
The argument -e is now set in both scripts to exit the scripts with non-
zero status if case any of their commands fail.

[ghost]

This is a backport of #544 for release 2018.10.1

[codecov]

Codecov Report

Merging #552 into release-2018.10 will increase coverage by 0.06%.
The diff coverage is n/a.

@@                 Coverage Diff                 @@
##           release-2018.10     #552      +/-   ##
===================================================
+ Coverage            64.87%   64.93%   +0.06%     
===================================================
  Files                  213      213              
  Lines                13833    13833              
===================================================
+ Hits                  8974     8983       +9     
+ Misses                4859     4850       -9

Impacted Files	Coverage Δ
.../theano/optimizers/conjugate_gradient_optimizer.py	74.05% <0%> (+0.63%)	⬆️
garage/envs/mujoco/gather/gather_env.py	57.91% <0%> (+1.34%)	⬆️
garage/theano/optimizers/first_order_optimizer.py	85.5% <0%> (+1.44%)	⬆️
garage/sampler/stateful_pool.py	69.23% <0%> (+2.3%)	⬆️

---

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[coveralls]

Coverage increased (+0.06%) to 65.385% when pulling ecf9d55 on backport-544 into 145733e on release-2018.10.