databases/rrdtool: Update to 1.7.2

Update databases/rrdtool to 1.7.2
Change USES=gnome to be added regardless of options, it's needed in all
cases.

Changelog:
https://github.com/oetiker/rrdtool-1.x/blob/v1.7.2/CHANGES

PR: 238832
Submitted by: amdmi3