! akka-cluster: metrics collector improvements - resolve #16121

in our experience, sigar either fails to load, or loads and calls do not fail
however, returning "sometimes JMX" and sometimes SIGAR would produce
meaningless data stream since they might report data on different scales

this check during construction
https://github.com/akka/akka/pull/16354/files#diff-d526b353336f96e0c9f04680068f193eR707
is supposed to simulate runtime collection and verify if sigar is usable

either way, silencing the failures in the monitoring data stream which one uses to detect system health seems like a bad idea. if sigar has failures it better be fixed as build/deploy issue.

I understand you seek core akka stability, but to us it looks like "let it crash" case. 

I see the following ways out:
1) let sigar fail and let it crash akka, jvm, and cause instance restart
2) bring the ```try``` back , but introduce scary ```error``` level logging

WDYT?