CI failover: s3compact cannot be triggered when diskcache is enabled

[YunhuiChen]

Describe the bug (描述bug)

To Reproduce (复现方法)

Expected behavior (期望行为)

Versions (各种版本)
OS:
Compiler:
curve-mds:
curve-chunkserver:
curve-snapshotcloneserver:
curve-sdk:
nebd:
curve-nbd:

Additional context/screenshots (更多上下文/截图)

[h0hmj]

when diskcache write cache is enabled, metadata maybe newer than data in s3, read will fail

pr #1006