Azure Blob Storage Client Library for Go

[ahmetb]

This contains set of commits to implement a blob storage client. This is mainly required for Azure Storage Driver for docker/docker-registry's new implementation.

Mostly the parts that would be required to the driver are implemented. Therefore some of the parts are not implemented yet. These are:

• Blob/container leases
• Operations on Page Blobs
• Snapshot blob
• Abort blob copy
• Set/Get blob/container metadata
• Set/Get container ACL
• Get/Set blob service properties
• Get Blob Service Stats

On the other hand most of the basic functionality and Block Blob methods are provided within the library. The storage service authentication code is inherited from packer-azure repo and I wrote unit tests around those to verify their functionality. packer-azure should start using this. (cc: @paulmey)

This package has no dependency to the rest of the repo at all. I could not find any reusable parts. Would be good if we can take this in as soon as possible. Once merged, feel free to list me as a maintainer for this package, I'd happily code-review.

Ideally we should not be breaking this package since all distributions of docker-registry will take a dependency on this package soon. If you guys are planning to set up a CI, I configured unit tests to work with an Azure storage account name/key passed through env. It tests the blob operations on a real storage account.

cc: @jeffmendoza @johngossman

[ahmetb]

@hopetobelievein thanks!