Add Unit Tests

[ob1dev]

Add Unit Tests.

1. Add the Sitecore.Azure.Diagnostics.Tests project based on the Unit Test Project template.
2. Tests must cover at least the logging and cleanup functionality.
3. Use the Azure Storage Emulator.
4. Most likely the Sitecore.Azure.Diagnostics project need to be refactored to get rid of the statics classes and methods.

[ob1dev]

Unfortunately, Azure Storage Emulator doesn't support Append Blob yet:
https://feedback.azure.com/forums/217298-storage/suggestions/10643412-provide-support-for-append-blobs-in-the-azure-stor