cmd/flux-wreck: check state and return codes in attach

In flux-wreck attach, do not open stdin if job is already
completed. When opening stdin, check return code from
io watcher and die on failure.

src/cmd/flux-wreck

@@ -63,6 +63,7 @@ prog:SubCommand {
  },
  handler = function (self, arg)
     local id = check_jobid_arg (self, arg[1])
+    local state = f:kvs_get ("lwj.%d.state")
     local taskio, err = wreck.ioattach {
         flux = f,
         jobid = id,
@@ -74,15 +75,18 @@ prog:SubCommand {
     if not taskio then
         self:die ("Failed to connect to job %d: %s\n", id, err)
     end
-    local kz, err = f:kz_open ("lwj."..id..".input.files.stdin", "w")
-    if kz then
-        f:iowatcher {
-            fd = posix.fileno (io.input()),
-            handler = function (iow, r)
-                if r.data then kz:write (r.data) end
-                if r.eof  then kz:close () end
-            end
-        }
+    if state ~= "complete" and state ~= "reaped" then
+        local kz, err = f:kz_open ("lwj."..id..".input.files.stdin", "w")
+        if kz then
+            local iow, err = f:iowatcher {
+                fd = posix.fileno (io.input()),
+                handler = function (iow, r)
+                    if r.data then kz:write (r.data) end
+                    if r.eof  then kz:close () end
+                end
+            }
+            if not iow then self:die ("error opening stdin: %s\n", err) end
+        end
     end
     if not taskio:complete() then f:reactor () end
     if self.opt.s then