EBLOB_AUTO_INDEXSORT eblob flag

New EBLOB_AUTO_INDEXSORT flag which enables sorting blob's index after the blob is closed. Extended running eblob_stress with EBLOB_AUTO_INDEXSORT flag.

Also added stat_file_time and stat_file_error to json statistics which can be used for determining hardware issues.
Does this mean that we skip file updates found in binary log if key was removed for example?
Or when is it possible that key can not be found in the sorted index?
Since it is printed at debug level, is this a very common operation?