#build steps:
1. 
#cp ./grub2-res.tar.gz /root/rpmbuild/SOURCES/
2.
rpmbuild -bb ./grub2-xcat.spec


#notes:
the grub2-res.tar.gz is generated by:
1.run the following cmd on a RHEL7-PPC64 node:
#grub2-mknetdir  --net-directory=/tftpboot/
#cd /tftpboot/boot/grub2/
#tar -czvf /tmp/grub2-res.tar.gz ./powerpc-ieee1275/