(#13396) Unify ifconfig usage and lookup ifconfig path to fix support for recent net-tools

Without this patch applied linux systems with recent net-tools loose
support for ipaddress,macaddress and other network related facts.
This is due to a path change from /sbin/ifconfig to /bin/ifconfig.
This patch fixes this issue by unifying the lookup and execution of
ifconfig and testing where the ifconfig binary is installed.
Merge branch 'backport-gh-386' into 1.6.x
Add missing require for macaddress

This fixes the error "Could not retrieve macaddress: uninitialized constant
Facter::Util::IP"
Call correct function on IP in NetMask

This fixes the error "Could not retrieve netmask: wrong number of arguments (1
for 0)"
Merge pull request #392 from pcarlisle/fix-nettools

Fix nettools