ScyllaDB release: version 1.2.1

ScyllaDB 1.2.1 is a bugfix release that maintains backward compatibility and supports rolling upgrades, addressing several issues found in the previous version. Key improvements include the splitting of SSTables between shards after startup to prevent wastefulness during migrations, handling of disk space errors more conservatively, and better management of errors during startup. Additional fixes involve ensuring that the node gracefully shuts down when disk space runs out, correctly invalidating cache during nodetool refresh to prevent stale data reads, and resolving installation issues on RHEL 7.2. Contributions from various developers have enhanced the system's robustness, including modifications to logging levels and improvements in error handling with the row cache and startup processes.