Change blobstore interface to return error for validate

This is preperation to remove ApplyOptions and pass options into constructor

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>
Remove ApplyOptions and pass blobstore options into constructor

Validate() now returns the error originally returned by ApplyOptions

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