'free' on Fedora 23 will use MemAvailable to calculate its 'available'
field, but we are passing through the host's value. Set it to match
MemFree, which is what 'free' will do for older linux that don't have
MemAvailable

https://bugzilla.redhat.com/show_bug.cgi?id=1300781
(cherry picked from commit c7be484d)