gms: Add is_shutdown helper for endpoint_state class

It will be used by streaming manager to check if a node is in shutdown
status.

gms/endpoint_state.hh

@@ -43,6 +43,8 @@
 #include "gms/heart_beat_state.hh"
 #include "gms/application_state.hh"
 #include "gms/versioned_value.hh"
+#include <boost/algorithm/string/split.hpp>
+#include <boost/algorithm/string/classification.hpp>
 #include <experimental/optional>
 #include <chrono>
 
@@ -148,6 +150,20 @@ public:
         _is_alive = false;
     }
 
+    bool is_shutdown() {
+        auto app_state = get_application_state(application_state::STATUS);
+        if (!app_state) {
+            return false;
+        }
+        auto value = app_state->value;
+        std::vector<sstring> pieces;
+        boost::split(pieces, value, boost::is_any_of(","));
+        if (pieces.empty()) {
+            return false;
+        }
+        return pieces[0] == sstring(versioned_value::SHUTDOWN);
+    }
+
     friend std::ostream& operator<<(std::ostream& os, const endpoint_state& x);
 };