RAC-aware and DG health checks

1. Complete overhaul in function that controls backups concurrency - now it is based on lock files and if lock
2. RAC-awareness
3. DG health checks - separate for primary and secondary databases. Primary will run backups on Primary if Standby is stale (even if asked to run backups only on Standby so we don't have stale backups)
4. Many other smaller changes