VMware: fix race for datastore directory existence

Treat the exception that is raised when creating a directory
and it already exists. This may happen due to two processes trying
to create the same directory at the same time.

Change-Id: Ia0ebd674345734e7cfa31ccd400fdba93646c554
Closes-bug: #1266579
Merge "VMware: fix race for datastore directory existence"