Plugins with multiple config policy nodes may cause a panic

[jcooklin]

When there are multiple config policy nodes
and there exists a metric which does not fall under any of the policies
and the root node does not contain a policy

The following example causes a panic since no policies apply to /intel/abc/baz.
metric types
/intel/abc/foo
/intel/def/bar
/intel/abc/baz

config at
/intel/abc/foo
/intel/def/bar

root
/intel