[pgm] Implement clone using CloneCommand

Change-Id: I56699b7bf9a71f673cb308d3015f51de5b06c1d9
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
[pgm] Add option --bare to clone command

Change-Id: I528491e3e20d3c9ebe37fe3cd2bf85b4644d8698
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>