Improve copy of atlas.war

Atlas Metadata Server's start script in Ambari includes a step to copy atlas.war from the default location to the expanded_webapp_dir. This is performed using File(content=StaticFile), which reads and writes the contents of the war file to/from memory. It may take 1-3 seconds to perform, and is done even if the source and target files are the same, because there is no check on the paths.

This could be improved:

1. Use cp to copy
2. Skip the operation if source and target are the same