Metrics need to include peer name

[jacksontj]

The metrics copied over in https://github.com/jacksontj/memberlistmesh/blob/master/cluster.go#L359 register with global names, which is an issue if you want to register 2 different memberlistmeshs in the same process. These should include the static label of the peer name (so we'd only have the issue if you tried to register 2 things with the same name).