Tests: update to Lucene 4.9.0

Closes #24.
Update to Azure Java SDK 0.4.6

Latest Azure Java SDK is 0.4.6 when looking at http://search.maven.org/#browse%7C-589510877

Closes #25.
`_` is a forbidden character for container (repository)

According to [Containers naming guide](http://msdn.microsoft.com/en-us/library/dd135715.aspx):

> A container name must be a valid DNS name, conforming to the following naming rules:
>
> * Container names must start with a letter or number, and can contain only letters, numbers, and the dash (-) character.
> * Every dash (-) character must be immediately preceded and followed by a letter or number; consecutive dashes are not permitted in container names.
> * All letters in a container name must be lowercase.
> * Container names must be from 3 through 63 characters long.

We need to fix the documentation and control that before calling Azure API.
The validation will come with issue #27.

Closes #21.
Wrong exception thrown when snapshot doesn't exist

As for https://github.com/elasticsearch/elasticsearch-cloud-aws/issues/86, we should raise a `SnapshotMissingException`.

Closes #23.
listBlobsByPrefix uses a wrong path

When listing existing blobs for an azure repository, `path` to look at is incorrectly computed which leads to 404 errors.

Closes #26.