Clean VMX step should always remove floppy.

:warning: While I'm pretty sure of the issue from the failing, then fixed unit test, I still need to run a complete build to see if this truly fixes the issue :warning: 

When using the VMX builder its possible for the source machine to have a floppy configured which gets cloned to the new VM Packer spins up. When the new VM's Packer config doesn't have a floppy_files config entry, the Packer clean VMX step fails to remove the floppy disk from the new VM. This can cause build failures, for example with the vsphere post processor; generating errors like:
```
* Post-processor failed: Failed: exit status 1
Error: File (/home/teamcity/tmp/buildTmp/packer941120499) could not be found.
```
Opening the cloned VM's VMX file you can clearly see it has a floppy entry from the source machine's VMX file (exact same path) even though the Packer config contains no floppy_files entry.