Execute almost all the process of the `gem` task in `GemCopyAction`

[dmikurube]

AbstractArchiveTask is expected to "read" the original data, and write into the destination archive, in its CopyAction. Currently, the process is done by running "copy", and executing JRuby in Gem, and then move the archive generated by JRuby to the destination path.

The process should be done in GemCopyAction to be compliant.