TokenCache.dat not created in profile initialization

[markcowl]

Description

When there is no TokenCache.dat file, we do not create a new one at profile initialization, because we create a cache using data of zero length. Instead we need to initialize the TokenCacheData with a default TokenCache here: https://github.com/Azure/azure-powershell/blob/preview/src/Common/Commands.Common.Authentication/AzureSessionInitializer.cs#L62

• Update AzureSessionInitializer to initialize the token cache with the default token cache contents rather than empty contents when the token cache file does not exist
• Add a test with a non-existent TokenCache that verifies correct TokenCache creation in AzureSessionInitializer

Cost: 2

[markcowl]

Fixed. Will ship in next release