Generate key for StorageAccount operations if none provided

[djberg96]

At the moment we require a storage account key for various storage account operations. It appears that Azure will alternatively accept an SAS token. Update the StorageAccount model to generate one automatically if a key isn't provided.

[djberg96]

With managed disks becoming the way of the future, I imagine this will be less and less of an issue. Still, I'll leave it open for now.

[djberg96]

Actually, in order to generate an SAS we still need a key. What I should have said is that users should be allowed to provide their own SAS for cases where they don't have the key information, but a signature has been provided to them.

In such cases we would not rely on the key, but would simply pass along the SAS as part of the URL, e.g. https://myaccount.blob.core.windows.net/sascontainer/sasblob.txt?sv=2015-04-05&st=2015-04-29T22%3A18%3A26Z&se=2015-04-30T02%3A23%3A26Z&sr=b&sp=rw&sip=168.1.5.60-168.1.5.70&spr=https&sig=Z%2FRHIX5Xcg0Mq2rqI3OlWTjEg2tYkboXr1P9ZUXDtkk%3D

However, upon further reflection I think this is rather a moot point, since to get the object in the first place you have to have the proper credentials. If you have the proper credentials, you have access to the key. Perhaps someday someone will request it as a feature, but until then I'm closing this.