Disk metrics should include device name instead of mountpoint

[tonydewan]

As it stands now, disk metrics collected by instrumentald will look like:

system.<hostname>.disk.<mount-point>.<metric>

Where mount-point will look like -, -boot, etc. It would be more useful and readable if it used the device name instead, or:

system.<hostname>.disk.<device-name>.<metric>

[tonydewan]

We have a PR outstanding on telegraf to enable this change.

[janxious]

This was updated upstream inm telegraf and in instrumentald