sysutils/ganglia-monitor-core: Upgrade to 3.7.2, disable python modules

Ganglia python modules require python 2.x, which is being removed from
the ports tree. Ganglia is no longer being developed upstream and upgrading
to python 3 appears to be fairly involved. Hence, I'm disabling python
modules in order to keep the port alive through the python 2 removal.

PR: 249772
Reported by: swills