When we catch an exception, print it to stderr before calling MPI.Abort

Previously, we were printing to stdout, but this makes it more likely
for the error message and stack trace to get lost, e.g. when
`quietoutput()` is used in the tests.

moment_kinetics/src/moment_kinetics.jl

@@ -148,8 +148,8 @@ function run_moment_kinetics(to::Union{TimerOutput,Nothing}, input_dict=Dict();
         # Stop code from hanging when running on multiple processes if only one of them
         # throws an error
         if global_size[] > 1
-            println("$(typeof(e)) on process $(global_rank[]):")
-            showerror(stdout, e, catch_backtrace())
+            println(stderr, "$(typeof(e)) on process $(global_rank[]):")
+            showerror(stderr, e, catch_backtrace())
             flush(stdout)
             flush(stderr)
             MPI.Abort(comm_world, 1)