SnapshotFileCache causes too many cache refreshes

Right now we decide whether to refresh the cache based on the lastModified timestamp of all the snapshots and those "running" snapshots which is located in the /hbase/.hbase-snapshot/.tmp/<snapshot> directory

We ran a ExportSnapshot job which takes around 7 minutes between creating the directory and copying all the files.

Thus the modified time for the
/hbase/.hbase-snapshot/.tmp directory was 7 minutes earlier than the modified time of the
/hbase/.hbase-snapshot/.tmp/<snapshot> directory

Thus the cache refresh happens and doesn't pick up all the files but thinks its up to date as the modified time of the .tmp directory never changes.

This is a bug as when the export job starts the cache never contains the files for the "running" snapshot and will fail.