thrift: Omit regular columns for dynamic CFs

This patch skips adding the auto-generated regular column when
describing a dynamic Column family for the describe_keyspace(s) verbs.

Signed-off-by: Duarte Nunes <duarte@scylladb.com>
Message-Id: <1469091720-10113-1-git-send-email-duarte@scylladb.com>
(cherry picked from commit a436cf945c)

thrift/handler.cc

@@ -1041,7 +1041,7 @@ private:
             }
             cf_def.__set_comment(s->comment());
             cf_def.__set_read_repair_chance(s->read_repair_chance());
-            if (s->regular_columns_count()) {
+            if (!s->thrift().is_dynamic()) {
                 std::vector<ColumnDef> columns;
                 for (auto&& c : s->regular_columns()) {
                     ColumnDef c_def;