Put confdir in the params class, and more..

Fix a bunch of warnings whne using the bind::updater class by moving confdir to
the params class. In order for this to work, the bind and bind::updater classes
both now inherit from params. Also, fix the default value for
managed_key_directory to something that's actually falsey.

spec/fixtures/hiera/common.yaml

@@ -1,3 +1,3 @@
 ---
-bind::confdir: '_CONFDIR_'
+bind::params::confdir: '_CONFDIR_'
 bind::namedconf: '_NAMEDCONF_'