`Mean` metrics missing

[alexjfisher]

Instead of not matching both Mean and MeanRate, the effect of d4809e3 seems to be no metrics for Mean collected at all (at least with the current version of jmx_exporter and Puppetserver 6).

Looks like you can't match the end of the string after the word Mean because it's not actually the end of the string. The string actually ends with a : and the metric value.

ie

- pattern: 'puppetserver<name=puppetlabs.puppet6.compiler><>(Max|Min|Mean|StdDev|50thPercentile|75thPercentile|95thPercentile|99thPercentile):'

works for me.