Improved readability of block log artifacts creation messages
Currently following messages are generated when new block log & artifacts files are created (due to e.g. appending first block of a new million in split file mode):
block_log.cpp:230 open ] Opening blocklog /home/hived/datadir/blockchain/block_log_part.0093 in read write mode ...
block_log_artifacts.cpp:247 set_block_num_to_fil ] Setting _block_num_to_file_pos_offset to 92000000
block_log_artifacts.cpp:411 open ] Opening artifacts file /home/hived/datadir/blockchain/block_log_part.0093.artifacts in read & write mode ...
block_log_artifacts.cpp:418 open ] Could not find artifacts file in /home/hived/datadir/blockchain/block_log_part.0093.artifacts. Creating new artifacts file ...
The last message may confuse the user to think that the artifacts file was expected to exist (it wasn't) but was not found due to some murky error. This MR suppresses the last message when new block log file has been created.