Added write_to_file function

Author: dlcole3

src/distributed/optigraph.jl

@@ -944,4 +944,13 @@ function MOI.Utilities.drop_optimizer(rgraph::RemoteOptiGraph)
         MOI.Utilities.drop_optimizer(lgraph)
     end
     return fetch(f)
+end
+
+function JuMP.write_to_file(rgraph::RemoteOptiGraph, filename::String)
+    darray = rgraph.graph
+
+    f = @spawnat graph.worker begin
+        lgraph = Plasmo.local_graph(darray)
+        JuMP.write_to_file(lgraph, filename)
+    end
 end