[build] add --enable-dev-tools configure flag

This builds tools that I want to keep in the same code base, but not
intended for general release.

thin-provisioning/commands.h

@@ -70,6 +70,13 @@ namespace thin_provisioning {
 		virtual int run(int argc, char **argv);
 	};
 
+	class thin_generate_metadata_cmd : public base::command {
+	public:
+		thin_generate_metadata_cmd();
+		virtual void usage(std::ostream &out) const;
+		virtual int run(int argc, char **argv);
+	};
+
 	void register_thin_commands(base::application &app);
 }