r=adilger

Ltest uses 'lbuild' to make rpms. When there're multiple ltestds do 'lbuild' at the same time, there's a good chance in a kernel or lustre building race if they build the rpms in a same directory. So we should use separate buildroot to avoid such issue. Also make changes to get 'make rpms' and 'make srpm' work smoothly with this change to lustre.spec.in.