Fix toolchain task failure due to undefined variable in renv.pp

Warning: Unknown variable: 'rpkgs'. (file: /home/centos/srcs/bigtop/bigtop_toolchain/manifests/renv.pp, line: 58, column: 21)
Warning: Arguments to Resource[] are all empty/undefined (file: /home/centos/srcs/bigtop/bigtop_toolchain/manifests/renv.pp, line: 58, column: 21)
Warning: Unknown variable: 'rpkgs'. (file: /home/centos/srcs/bigtop/bigtop_toolchain/manifests/renv.pp, line: 90, column: 12)
Error: Evaluation Error: Missing title. The title expression resulted in undef (file: /home/centos/srcs/bigtop/bigtop_toolchain/manifests/renv.pp, line: 90, column: 12) on node ip-172-31-197-233.ap-northeast-1.compute.internal