[Samba] Makerpms.sh changes for RH8

[Freeman, Peter (ERHS)]

The rpm build utilities have changed with Redhat 8.0.

I'm not sure if these changes have been noted in the current sources,
but the "makerpms.sh" script in the src/packaging/Redhat directory no
longer works with Redhat 8.0 without the change below.

The two lines at the end of the script need to have "rpm" changed to
"rpmbuild", the switches remain the same. You also need the "rpm-build" 
package installed.

Regards