Clean VMX step should always remove floppy.

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.
GH 1508 - Ensure Packer VMX is updated and saved

We need to ensure the VMWare process has exited before attempting to run VMX file cleanup steps, otherwise VMWare may overwrite our changes. While Packer does its best to ensure VMWare has exited, there's still a race condition on some OSs between VMWare flushing the VMX and Packer updating it. The workaround is to artifically wait 5 seconds.

When using the VMX builder its possible for the source machine to have a floppy and/or CD-ROM mounted which gets cloned to the new VM Packer spins up, but have no Packer configuration for those devices. With this change we always attempt to remove the mounted devices regardless of the Packer configuration.
Merge pull request #1504 from sneal/always-remove-vmx-floppy-entries

Clean VMX step should always remove floppy.