Fixes

Logs blob config and disk control flags in pretty format.
Added to eblob_backend counter `defrag_generation` that is increased after each time when blobs are defraged. It is used by code that could have TOC vs TOU race between cache lookup and writing a record.

Added string representation of want_defrag status of base to json statistics.
Fixed base size (bctl_size) in eblob_check_record - bctl->data_size is a valid size of closed blob, bctl->data_offset is an offset of open blob where new record should be written. In common way it is better to use the larger one.

Fixed defrag: restored sorting unsorted blobs even if defrag is not needed.

Sets errno if init has been failed - it is the one possible way to notify caller about which error is occurred.