Implement directory locks?

[msyriac]

Preferably, we want to avoid the following scenarios:

1. rsync is reading from a directory where the contents are changing, and so produces corrupted files at NERSC
2. Two or more different crons are running these scripts, and so sometimes two or more rsyncs are writing to the same NERSC directory

This can be achieved by locking the sync directories. Only drawback is that sometimes, this will not allow people making these products to write them to the sync directories.