Added tests for contrib.locked_file.

[theacodes]

Towards #212

This module beastly. It's only user is multistore_file and honestly I would be in favor of outright removing this and that from the library altogether.

These tests do not cover the platform-specific opener classes - I'd really like to hear some ideas on how to test those.

[theacodes]

@thobrla it seems that gsutil is a user of multistore_file here. How would you feel about us trying to remove this? It's a lot of code (and cruft) for a very specific use case. Is there a better storage option we can provide (sqlite?)

[thobrla]

I'm fine with removing both locked_file/multistore_file if a suitable alternative is provided. The requirement is to safely use a single credential across multiple processes and threads. If we can find a better cross-platform way to do that, I'm happy to port gsutil over (other incompatibilities notwithstanding).

[theacodes]

I'll start a separate issue for that, thanks, @thobrla.

[dhermes]

LGTM mostly

[theacodes]

Updated, should address most of your comments.

Thanks for the review. I have no idea what it is about this library but I just end up writing sloppy tests. :|

[dhermes]

LGTM more mostly

[theacodes]

Any qualms with merging this? Should we get @nathanielmanistaatgoogle? I'm just past caring on this one and would rather push for its removal if we can get gcloud cli and gsutil to play along.

[dhermes]

Ha sorry my last comment was meant to be a "go-ahead and merge" LGTM

[theacodes]

Ha. Fair enough. I'm still open to suggestions on testing the platform-specific stuff (mocks?) provided we don't vote it off the island.