VMware: fix broken mock of ds_util.mkdir

Change I788e33dbcb3dedc41831b976137607274b1c02ca introduced an
incorrect use of mock which had side-effects for other tests. This
change fixes it.

Change-Id: I71188ec7c12d51c2b4a253f13a5f51cc8bc0ae36
Merge "VMware: fix broken mock of ds_util.mkdir"