Port ssh functionality from 2016-patches, fix a property and add a test

• The ssh capabilities were only on the 2016-patches branch, this MR brings them to master too.
• The recent modernization had missed a this in the KeepFiles property.
• lcg-cp is no longer available so that part of the functionality has been removed.
• A test has been added.

I'll create a separate MR for 2018-patches.