monasca-grafana image is failing to build, blocking the gate

As seen here:

http://logs.openstack.org/03/625003/1/gate/kolla-build-centos-source/9b2454e/logs/build/000_FAILED_monasca-grafana.txt.gz

INFO:kolla.common.utils.monasca-grafana:Step 12/15 : RUN gem install fpm && curl -sSL -o /tmp/monasca-grafana.tgz ${monasca_grafana_url} && mkdir -p ${monasca_grafana_build_path} && tar --strip 1 -xvf /tmp/monasca-grafana.tgz -C ${monasca_grafana_build_path} && rm -f /tmp/monasca-grafana.tgz && cd ${monasca_grafana_build_path} && go run build.go setup && npm install && go run build.go build package && mv ${monasca_grafana_build_path}/dist /grafana_pkgs && rm -rf /grafana
INFO:kolla.common.utils.monasca-grafana: ---> Running in 98030f2476ac
INFO:kolla.common.utils.monasca-grafana:Building native extensions. This could take a while...
INFO:kolla.common.utils.monasca-grafana:Successfully installed json-1.8.6
INFO:kolla.common.utils.monasca-grafana:Successfully installed cabin-0.9.0
INFO:kolla.common.utils.monasca-grafana:Successfully installed backports-3.11.4
INFO:kolla.common.utils.monasca-grafana:Successfully installed arr-pm-0.0.10
INFO:kolla.common.utils.monasca-grafana:Successfully installed clamp-1.0.1
INFO:kolla.common.utils.monasca-grafana:Building native extensions. This could take a while...
INFO:kolla.common.utils.monasca-grafana:ERROR: Error installing fpm:
INFO:kolla.common.utils.monasca-grafana: ERROR: Failed to build gem native extension.
INFO:kolla.common.utils.monasca-grafana: /usr/bin/ruby mkrf_conf.rb
INFO:kolla.common.utils.monasca-grafana:rake RUBYARCHDIR=/usr/local/lib64/gems/ruby/childprocess-1.0.0/lib RUBYLIBDIR=/usr/local/lib64/gems/ruby/childprocess-1.0.0/lib
INFO:kolla.common.utils.monasca-grafana:sh: rake: command not found
INFO:kolla.common.utils.monasca-grafana:Gem files will remain installed in /usr/local/share/gems/gems/childprocess-1.0.0 for inspection.
INFO:kolla.common.utils.monasca-grafana:Results logged to /usr/local/share/gems/gems/childprocess-1.0.0/ext/gem_make.out
INFO:kolla.common.utils.monasca-grafana:
INFO:kolla.common.utils.monasca-grafana:Removing intermediate container 98030f2476ac
ERROR:kolla.common.utils.monasca-grafana:Error'd with the following message
ERROR:kolla.common.utils.monasca-grafana:The command '/bin/sh -c gem install fpm && curl -sSL -o /tmp/monasca-grafana.tgz ${monasca_grafana_url} && mkdir -p ${monasca_grafana_build_path} && tar --strip 1 -xvf /tmp/monasca-grafana.tgz -C ${monasca_grafana_build_path} && rm -f /tmp/monasca-grafana.tgz && cd ${monasca_grafana_build_path} && go run build.go setup && npm install && go run build.go build package && mv ${monasca_grafana_build_path}/dist /grafana_pkgs && rm -rf /grafana' returned a non-zero code: 1