Use FileUtils.mv() instead of File.rename() function

File.rename() raises the following error when the file is renamed to an other
partition: Invalid cross-device link
Rename --version option to --appversion, fixes igalic#1

Rename --version option to --appversion to avoid conflict with mco own
--version option
Immediately fail if the SHA1 of the artefact is not matching

Immediately fail if the SHA1 of the artefact is not matching in the
download() function
Use mcollective run() function instead of system()

Looking that the documentation, this seems to be the prefered way to run
external commands
Merge pull request #2 from bigon/to_upstream

Please consider the following changes