Unexpected metric names when cluster name contains dot

Title: Unexpected metric names when cluster name contains dot

Description:

When cluster name contains dot, cluster-specific metric names are unexpected.

Repro steps:

Create a cluster with dots in its name, e.g. foo.example.com, and then look for cluster metrics like envoy.cluster.upstream_rq_xx

Expected:

The metric should be named envoy.cluster.upstream_rq_xx with tag envoy_cluster_name=foo.example.com

Actual:

The metric is named envoy.cluster.example.com.upstream_rq_xx with tag envoy_cluster_name=foo