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.

builder/vmware/step_clean_vmx.go

@@ -55,12 +55,12 @@ func (s stepCleanVMX) Run(state multistep.StateBag) multistep.StepAction {
 			continue
 		}
 
-		filenameKey := match + ".filename"
+		filenameKey := match + "filename"
 		if filename, ok := vmxData[filenameKey]; ok {
 			if filename == isoPath {
 				// Change the CD-ROM device back to auto-detect to eject
 				vmxData[filenameKey] = "auto detect"
-				vmxData[match+".devicetype"] = "cdrom-raw"
+				vmxData[match+"devicetype"] = "cdrom-raw"
 			}
 		}
 	}