patch review: storage check for retrace.f.o

[Miroslav Suchý]

I want to set up monitoring of free space on /srv of retrace.fedoraproject.org. It is huge
volume therefore normal
check_disk_/srv does not have sense. I created new check, but it is my first time working
with nrpe. I would welcome if
someone can review it, before I push it.
Patch is in the attachment.

Miroslav