Always build the same input files to a stable output

[johan]

#299, but for the preview branch. As I haven't tested this and don't generally speak a lot of python, vet with extra caution.

[shaka-bot]

Testing in progress...

[shaka-bot]

Failure:

+ ./build/all.py
101 files checked, no errors found.
+ git checkout github/master -- karma.conf.js
+ export NODE_PATH=/usr/local/lib/node_modules
+ NODE_PATH=/usr/local/lib/node_modules
+ xvfb-run karma start --single-run --no-colors --reporters junit,dots --log-level disable --browsers Chrome
Chrome 49.0.2623 (Linux 0.0.0): Executed 0 of 0 ERROR (0.003 secs / 0 secs)

[joeyparrish]

Let me investigate. Our build bot is still fairly new, so this might be the bot's fault.

[johan]

Seems it builds happily at my end (and the exact same output, save the git hash) both before and after the change, so that sounds likely. This change may not even be necessary for the python version, if its filesystem traversing api:s already are defined to return files in sorted order.

[shaka-bot]

Testing in progress...

[joeyparrish]

There was a bug in the bot's job script. We made a mistake in the v1-v2 transition. Should be working for both branches now.

[shaka-bot]

All tests passed!

[joeyparrish]

@johan Thanks so much!