More accurate disk percent usage ignoring privileged bytes Closes #156

[SaviourSelf]

Pull Request Checklist

Is this in reference to an existing issue?

Yes, see issue: https://github.com/sensu-plugins/sensu-plugins-disk-checks/issues/156

General

• [x] Update Changelog following the conventions laid out here

• [x] Update README with any necessary configuration snippets

• [x] Binstubs are created if needed

• [x] RuboCop passes

• [x] Existing tests pass

New Plugins

N/A

Purpose

Purpose is to more accurately reflect the output of the df linux command.

Known Compatibility Issues

No known compatibility issues.

Example output

Windows

df -h
Filesystem      Size  Used Avail Use% Mounted on
rootfs          931G  856G   75G  92% /

./check-disk-usage.rb -p '(\/var|\/run|\/sys|\/dev|\/mnt)' -r
CheckDisk WARNING: / 92.99% bytes usage (855.99 GiB/930.45 GiB)

Linux

df -h
Filesystem      Size  Used Avail Use% Mounted on
rootfs          143G   28G  109G  21% /

./check-disk-usage.rb -w 10 -r
CheckDisk WARNING: / 21.31% bytes usage (27.55 GiB/142.91 GiB)
./check-disk-usage.rb -w 10
CheckDisk WARNING: / 19.28% bytes usage (27.55 GiB/142.91 GiB)

[majormoses]

released: https://rubygems.org/gems/sensu-plugins-disk-checks/versions/5.1.2