Adds option for lazy connection to swift

[pomegranited]

Instead of connecting to SWIFT on storage init, this adds an option to allow the SWIFT connection to be created only when required.

Django takes great care to initialise Storage classes lazily, and so connecting on creation is generally a valid option. However there are some cases where this is difficult to do, e.g., when using FileField.storage, the Storage instance is instantiated on model import time, which can result in unintended SWIFT authentication/connections.

Reviewer

• @smarnach

[codecov-io]

Codecov Report

Merging #97 into master will increase coverage by 0.12%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #97      +/-   ##
==========================================
+ Coverage   97.77%   97.89%   +0.12%     
==========================================
  Files           1        1              
  Lines         225      238      +13     
==========================================
+ Hits          220      233      +13     
  Misses          5        5

Impacted Files	Coverage Δ
swift/storage.py	97.89% <100%> (+0.12%)	⬆️

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[smarnach]

👍 Looking good to me. I've read through the code and tested that it still works for our use case (an Open edX instance).

I'm wondering whether there is any disadvantage to connecting lazily, or whether lazy connections should be the default, but it's probably safer to keep the current behaviour.

[pomegranited]

Hi @dennisv ! Would you consider merging this PR? Please let me know if you need more information or tests added.

[pomegranited]

Thank you @dennisv !

[dennisv]

It's also pushed to PyPI:
https://pypi.python.org/pypi/django-storage-swift/1.2.18

[pomegranited]

So quick -- awesome!