typo fix
Change default param for nic or group to empty string

to match hash in nic_option or group_option assignments.
Othwerwise, could end up with puppet output like:
  Debug: Executing '/usr/sbin/pcs resource create ip-192.168.200.50 IPaddr2 ip=192.168.200.50 cidr_netmask=32 nic=nil ...
Merge pull request #3 from cwolferh/more_stuff

typo fix