Add option to prevent gmetad from generating summaries for sFlow VM metrics

This patch adds a new "unsummarized_sflow_vm_metrics" config option to gmetad
to prevent generating summaries for metrics that appears to be sFlow VM metrics.

A metric is determined to be an sFlow VM metric when the metric name contains
character '.' followed by character 'v'.

Ex: xenvm1.vcpu_num is an sFlow VM metric, vnode_cpu_num is not.
if using graphite_path, use the specified source/host/metric template
instead of just the cluster name
clean up metrics with spaces in them like we do for cluster names
mirror case_sensitive_hostnames logic when using graphite_path
Merge pull request #113 from siboulet/master

Add option to prevent gmetad from generating summaries for sFlow VM metrics
Merge pull request #114 from cburroughs/graphite-path-fix

Graphite path fix