expose ipmilan lanplus options to end user

The reason there are two params rather than just one, is we want to allow the user to *not* pass in the lanplus argument at all in the command line to "pcs stonith create..." (i.e. $fence_ipmilan_expose_lanplus is false), or just pass in lanplus="" (i.e. $fence_ipmilan_lanplus_options is empty but $fence_ipmilan_expose_lanplus is true ), or lanplus="1" ($fence_ipmilan_lanplus_options is 1), etc.