os/FileStore: set replay guard on collection creation

This avoids a problematic sequence like:

 - rename A/ -> B/
 - remove B/1...100
 - destroy B/
 - create A/
 - write A/101...
 <crash>
 - replay A/ -> B/
 - remove B/1...100  (fails but tolerated)
 - destroy B/        (fails with ENOTEMPTY)

The solution is to skip replay of the initial collection rename
operation.

Signed-off-by: Sage Weil <sage@inktank.com>