fix Workgroup being overwritten by realm name. bnc#902302

don't set the Workgroup with the name returned from Samba.GetWorkgroupOrRealm
otherwise for non ADS config the realm/domain name will be set for Workgroup.
Merge pull request #37 from noelpower/bnc#902302_SLE12

fix Workgroup being overwritten by realm name. bnc#902302