Change default path for dupload

In current version plugin always stores dupload file in /etc. This solution has several flaws.
* Build robot must have admin right for `mv` operation (potentially, dangerous).
* This config will be override by config in ~/.dupload (if exists).

I change this logic:
* If build robot has home dir, plugin stores config in ~/.dupload.
* Otherwise, stores it in /etc/dupload.
Are you sure this runs properly on the slave? Looks like you check the ``user.home`` property on the master but run the command on the slave..