Revert "VMware: fix race for datastore directory existence"

This reverts commit 743b74d59d3279478c512a0a559642b1d05284bc,
which introduces a race condition when creating the initial
instance image. Since _mkdir() no longer fails if the directory
exists, two computes racing to create the same image will
result in either corrupted data, lost data, or a strange
failure later on.

Change-Id: Ic646a01b2f96b1341af38b69c372875a95263bad
Closes-bug: #1284312
Merge "Revert "VMware: fix race for datastore directory existence""