v1.2.1-rc0

new features

• curve-nbd: support simulate 512-byte logical/physical block device
• curve-nbd: prevent mounted device to unmap
• curve-nbd: add auto mount options
• nebd: support multi-instances for different user
• client: retry allocate segment until success
• mds: schedule pending online chunkserver

bug fix

• ansible: backup and recover curvetab
• debian package: backup and recover curvetab
• scripts: fix potential overflow when cnovert ip to value
• client: fix segment in SourceReader
• client: explicit stop LeaseExecutor in FileInstance::UnInitialize
• curve-nbd: fix concurrent nbd map
• snapshotclone: fix cancel task lost
• tools: remove copyset data after remove peer
• mds: modify stale heartbeat update error with warning
• chunkserver: fix config change epoch update error