Support perfdata data in the --nagios output

[arthurzenika]

PerfData is a mecanism to add to the OK/KO status some data about performance (or other)

https://assets.nagios.com/downloads/nagioscore/docs/nagioscore/3/en/perfdata.html

In some cases this PerfData can be reused in supervision (or with a graphite-grafana setup).

It would be nice for testinfra to support this sort of data in the --nagios output.

[arthurzenika]

We could take a look at nagioplugin python library

• https://pythonhosted.org/nagiosplugin/glossary.html#term-performance-data
• https://pythonhosted.org/nagiosplugin/api/intermediate.html?highlight=performance#module-nagiosplugin.performance
• check_load example https://pythonhosted.org/nagiosplugin/tutorial/check_load.html