Test result storage improvements and impact on upgrading to Team Foundation Server 2017

Introduces a new, more compact, and efficient schema for storing test results in TFS 2017, leading to a 5x-8x reduction in storage footprint for test result data. This change necessitates a data migration during the upgrade process, potentially increasing upgrade times. Provides guidelines for administrators to reduce upgrade window duration, including configuring test retention policies and using the TFSConfig.exe tool for pre-upgrade cleanup. For VSTS, the migration is transparent and phased.