provide a reference snapshot

[ccanepa]

Albeit snapshots will vary with hw/sw combinations, a reference snapshot set should be provided to know if a new testbed is even in the ballpark.

• 00_init should inject the neccesary data into work/
• code in do_test should change so the cache key for the reference snapshot can't match any possible snapshot in the current testbed, maybe adding a '@' in the key
• current size for a snapshot dir is aprox 16MB, so bareable in terms of git clone

[ccanepa]

Done, commit d1f71367 is a good one, ore anything with release version 0.7+