qa: add validation stage for deduplication.py

qa: add validation stage for deduplication.py

To validate sample-dedup actually works, validate() runs
separated thread from sample-dedup and verifies
two following things.
1. check sample-dedup starts properly.
2. check references of all the chunk objects' in chunk tier
   exists in designated base pool.
This routune repeats for max_valication_cnt times while
sample-dedup is running. If it doesn't raise any fail while the loop,
we can pretend sample-dedup works accurately.
If not, assert() will stop this test.

In case that a reference of chunk object doesn't exist in base pool,
validate() gives a second chance after repairing it (chunk-repair op)
to deal with false-positive reference inconsistency.

Signed-off-by: Sungmin Lee <sung_min.lee@samsung.com>