yamlinfo: use different dir to list all nodes

We used Dir.entries('/var/lib/puppet/yaml/node/') to get a list of all
nodes.  That dir is now empty.  Switch to using
Dir.entries('/var/lib/puppet/yaml/facts/').

Both are probably bad, but yamlinfo() should be phased out in favor of
hiera/puppetdb anyhow, so for now this is a temporary fix.