Add new rpm builder for CentOS6/RHEL6 and CentOS7/RHEL7.

CentOS6/pgpool-II-33: for pgpool-II 3.3.* and PostgreSQL 9.2, 9.3, 9.4
CentOS6/pgpool-II-34: for pgpool-II 3.4.* and PostgreSQL 9.2, 9.3, 9.4
CentOS7/pgpool-II-33: for pgpool-II 3.3.* and PostgreSQL 9.2, 9.3, 9.4
CentOS7/pgpool-II-34: for pgpool-II 3.4.* and PostgreSQL 9.2, 9.3, 9.4