Fix output directory creation

[desilinguist]

• We had a bug in the code where _locate_file() was being called and we were depending on its return value to decide whether to create the output directories or not. However _locate_file() raises an exception when the file doesn't already exist, so this was a total waste of time.
• I fixed the code so that we actually catch the exception for non-existent output directories and then use that to create the directories if needed.
• For the tests, I simply removed the pre-test manual creation of the output directory from test_output.py such that the automatic directory creation will be tested.

[coveralls]

Coverage increased (+0.2%) to 92.684% when pulling 9d0c8a9 on fix-output-directory-creation into 322749b on master.

[desilinguist]

Ugh, stupid coveralls! :(

[desilinguist]

@aoifecahill @Lguyogiro @benbuleong @jbiggsets This is now ready for review. Please actually try an experiment on your local machines with directories to make sure.

[Lguyogiro]

Looks good, and worked for me.

[desilinguist]

@benbuleong since you filled the original issue, can you please review this? @aoifecahill if you could test it too, it'd be great!

[benbuleong]

@desilinguist : Sure, I will review it by EOD

[aoifecahill]

Thanks, I tried it out and it worked for me :)