blob: properly handle offset writes when cfg.bsize is set

Reported by: shaitan@
EBLOB_NO_FOOTER and commit_ll

When we overwrite data not in-place then we copy only subset of old data
to the new blob, but if EBLOB_NO_FOOTER is set and we close blob right
after that write then last record will have disk_size pointing outside
of current base, because with EBLOB_NO_FOOTER eblob_write_commit_ll()
will exit without writing any data and so on next open data file will be
truncated effectively removing last base's record and logging:

     blob: malformed entry: position + data
     size are out of bounds: ...
tests: stress: added block size parameter
ci: added blocksize + nofooter tests