engine: resources: The kv resource can set un-mapped values

Previously the resource could only set values in a per-hostname
namespace, but for single, user-managed values, we'd like to be able to
control things entirely. Now this resource can do that.

examples/lang/states0.mcl

@@ -17,6 +17,7 @@ if $state == "one" or $state == "default" {
 	kv "${ns}" {
 		key => $ns,
 		value => "two",
+		mapped = true,
 	}
 	Exec["timer"] -> Kv["${ns}"]
 }
@@ -33,6 +34,7 @@ if $state == "two" {
 	kv "${ns}" {
 		key => $ns,
 		value => "three",
+		mapped = true,
 	}
 	Exec["timer"] -> Kv["${ns}"]
 }
@@ -49,6 +51,7 @@ if $state == "three" {
 	kv "${ns}" {
 		key => $ns,
 		value => "one",
+		mapped = true,
 	}
 	Exec["timer"] -> Kv["${ns}"]
 }