cubicweb-vcsfile #1347953 don't clone / pull up if we don't import revision content and repository-import = no [resolved]

since we don't need the local cache in such cases.

Also, this avoid error on our extranet when trying to set source_url to an url that is not accessible from the DMZ (only from the intranet where a CI dedicated instance run)

done in1.6.5
load left0.000
closed by#b8e9ce290b16 don't clone when not necessary (closes #1347953)