inject platform into infrastructure provider

Signed-off-by: Nick Wade <nwade@pivotallabs.com>
Remove infrastructure/platform delegates and use platform directly

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>
introduce NormalizeDiskPath to platform interface

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>
extract normalization of disk path from SetupEphemeralDiskWithPath

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>