VDI_RESET bug fix and versioned SM capabilities

This pull request fixes a bug with VDI_RESET, in which the VDI reset was triggered on migrate. It also deprecates the SM capabilities field in favour of features, which is a new SM field. A feature is a versioned capability. This allows clients to tell if xapi advertises VDI_RESET_ON_BOOT version 1, which has severe bugs, or version 2, which resolves those bugs.