Delay a random jitter period prior to request a Router ID for REED. (#554)

* Delay a random jitter period prior to request a Router ID for REED.

* Update Cert_5_1_09_REEDAttachConnectivity.py to pass Travis check.

* Add CLI to set/get the ROUTER_SELECTION_JITTER and update Certification scripts.

  - add 'posix-ncp' to allow failure list in .travis.yml.

src/cli/cli.hpp

@@ -194,6 +194,7 @@ private:
     void ProcessRouter(int argc, char *argv[]);
     void ProcessRouterDowngradeThreshold(int argc, char *argv[]);
     void ProcessRouterRole(int argc, char *argv[]);
+    void ProcessRouterSelectionJitter(int argc, char *argv[]);
     ThreadError ProcessRouteAdd(int argc, char *argv[]);
     ThreadError ProcessRouteRemove(int argc, char *argv[]);
     void ProcessRouterUpgradeThreshold(int argc, char *argv[]);