os/bluestore: Add new onode recovery method

os/bluestore: Add new onode recovery method

Added read_allocation_from_onodes_mt function
  (originally copied from read_allocation_from_onodes).
Added Decoder_AllocationsAndStatFS class
  (originally copied from ExtentDecoderpartial).

There are significant differences from originals:
- shared blobs are not scanned at all
- to not account allocations more than once,
  collisions are detected on SimpleBitmap level;
  only the first onode referencing shared blob will mark allocation
- Blobs are not preserved
- instead we remember only if blob or spanning blob was compressed

The underlying logic is make recovery faster and prepare for
multithread refactor.

Signed-off-by: Adam Kupczyk <akupczyk@ibm.com>