Copy files for balancing but remove source only after checksum of cop…

[pessimal]

…ied file matches source

[pessimal]

Makes things slower but helps me sleep at night. Maybe out of scope for tool as could be argued responsibility for file integrity lies with file system, just close if no interest.

[trapexit]

If I were to accept a change to support this it'd need to be optional and cleaned up. Shouldn't be using && like that and instead properly call subprocess call for each and compare exit codes.