Merge branch 'update-performance-metrics' into 'master'

Update performance metrics rake task and documentation

See merge request !268

doc/howto/performance_metrics.md

@@ -4,8 +4,8 @@ GitLab comes with a built-in performance metrics system. Metrics are
 collected by InfluxDB and visualized using Grafana.
 To use performance metrics in GitLab Development Kit you need a working
-Golang compiler and NPM installed. InfluxDB and Grafana consume about
-700MB of additional disk space (excluding metrics data).
+Golang compiler (at least v1.7) and NPM installed. InfluxDB and Grafana consume
+about 700MB of additional disk space (excluding metrics data).
 You need to have a working GDK installation before you install InfluxDB
 and Grafana.

grafana/Makefile

@@ -24,7 +24,7 @@ bin/grafana-server:	${GRAFANA_SOURCE}/build.go
 public:	bin/grafana-server
 	cd ${GRAFANA_SOURCE} && npm install
 	cd ${GRAFANA_SOURCE} && npm install grunt-cli
-	cd ${GRAFANA_SOURCE} && node_modules/grunt-cli/bin/grunt build
+	cd ${GRAFANA_SOURCE} && node_modules/grunt-cli/bin/grunt build --force
 	mv ${GRAFANA_SOURCE}/public_gen $@
 vendor: public