Ensure external tools can see our VMX changes.

There was a potential race condition between the VMX being written and a post-processor like the vsphere ovftool being able to correctly pickup the modified VMX file. The Sync call commits the current contents of the file to stable storage. This means flushing the file system's in-memory copy of recently written data to disk.
Always remove cdrom-image entries from VMX

When using the VMX builder its possible to have an existing ISO mounted that Packer doesn't know about from the packer config file, i.e. chaining a Packer VMX build from a Packer ISO build. With this change we always attempt to remove the mounted CD regardless of the Packer configuration.