snitch: Introduce and use get_location() method

There are some places out there that generate locator::endpoint_dc_rack
pair out of snitch's get_datacenter() and get_rack() calls. Generalize
those with snitch's new method. It will also be used by next patch.

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>

locator/snitch_base.hh

@@ -15,6 +15,7 @@
 #include <boost/signals2.hpp>
 #include <boost/signals2/dummy_mutex.hpp>
 
+#include "locator/types.hh"
 #include "gms/inet_address.hh"
 #include "inet_address_vectors.hh"
 #include "gms/versioned_value.hh"
@@ -70,6 +71,13 @@ public:
      */
     virtual sstring get_datacenter() const = 0;
 
+    locator::endpoint_dc_rack get_location() const {
+        return locator::endpoint_dc_rack{
+            .dc = get_datacenter(),
+            .rack = get_rack(),
+        };
+    }
+
     /**
      * returns whatever info snitch wants to gossip
      */