NRPE check reports OK, but status is CRITICAL

[Xav Paice]

Upgraded charm to master + build from the master of layer-ntpmon. On a host where no upstream servers can be reached, the check result was OK, but the text was accurate:

NRPE check reports OK, but status is CRITICAL: reachability is too low (0.00%) - must be greater than 50.00%

$ sudo chronyc sources
210 Number of sources = 20
MS Name/IP address Stratum Poll Reach LastRx Last sample
===============================================================================
^? b335.cxs.pw 0 10 0 - +0ns[ +0ns] +/- 0ns
^? ntp3.torix.ca 0 10 0 - +0ns[ +0ns] +/- 0ns
^? ntp1.exa-networks.co.uk 0 10 0 - +0ns[ +0ns] +/- 0ns
^? time.cloudflare.com 3 10 0 62h -1478us[-1478us] +/- 94ms
^? time.videxio.net 0 10 0 - +0ns[ +0ns] +/- 0ns
^? berlix.fraho.eu 0 10 0 - +0ns[ +0ns] +/- 0ns
^? 196.49.6.106 0 10 0 - +0ns[ +0ns] +/- 0ns
^? 192.33.214.47 0 10 0 - +0ns[ +0ns] +/- 0ns
^? server2.websters-compute> 0 10 0 - +0ns[ +0ns] +/- 0ns
^? 220-133-149-235.HINET-IP> 0 10 0 - +0ns[ +0ns] +/- 0ns
^? ntp02.maillink.ch 0 10 0 - +0ns[ +0ns] +/- 0ns
^? ntp4.inx.net.za 0 10 0 - +0ns[ +0ns] +/- 0ns
^? repository.habari.co.tz 0 10 0 - +0ns[ +0ns] +/- 0ns
^? bwntp2pool.bluewin.ch 0 10 0 - +0ns[ +0ns] +/- 0ns
^? ntp3.wirehive.net 0 10 0 - +0ns[ +0ns] +/- 0ns
^? uruz.org 0 10 0 - +0ns[ +0ns] +/- 0ns
^? chilipepper.canonical.com 0 10 0 - +0ns[ +0ns] +/- 0ns
^? alphyn.canonical.com 0 10 0 - +0ns[ +0ns] +/- 0ns
^? golem.canonical.com 0 10 0 - +0ns[ +0ns] +/- 0ns
^? pugot.canonical.com 0 10 0 - +0ns[ +0ns] +/- 0ns