Setting a specific file name as chart target does not work

[migmartri]

For example using

Target: mover.Target{
			Chart: mover.ChartSpec{
				Local: mover.LocalChart{
					Path: "/home/migmartri/Desktop/mariadb-10.0.2.relocated.tgz",
				},
			},
		},

Creates the file

'mariadb-10.0.2.relocated.tgz%!(EXTRA string=mariadb, string=10.0.2)' 

We should allow setting the output when using relok8s as library

cc/ @josvazg since we've talked about this before