Trivial bug fix in mechanism to clean installation ISOs for VMware builder

The resolution of Bug #608 still had issues.  This change removes a
superfluous period.

Testing Done:
- built packer with my change
- built VMware VMs and saw that the vmx file had the expected
  changes.
Merge pull request #685 from veshi/master

builder/vmware: trivial bug fix in mechanism to clean installation ISOs for VMware build...