Storage Classes and Co-location hints

[mlassnig]

Motivation

To help tape systems with colocation, we will pass two metadata hints per file:

storage_class:<classname> as a single value,

and group_hints:['<mostimportant>', .... , '<leastimportant>'] as an ordered list of string values.

[bari12]

@mlassnig What's the status on this? I doubt that FTS will forward this properly to Tape, but can't we already add it to the transfer requests?