Fix error handling in nodeshell

nodeshell needed to process errors correctly, and not assume databynode would be there.

confluent_client/bin/nodeshell

@@ -55,10 +55,15 @@ def run():
     all = set([])
     pipedesc = {}
     pendingexecs = deque()
+    exitcode = 0
+
 
     for exp in c.create('/noderange/{0}/attributes/expression'.format(args[0]),
                         {'expression': cmdstr}):
-        ex = exp['databynode']
+        if 'error' in exp:
+            sys.stderr.write(exp['error'] + '\n')
+            exitcode |= exp.get('errorcode', 1)
+        ex = exp.get('databynode', ())
         for node in ex:
             cmd = ex[node]['value'].encode('utf-8')
             cmdv = ['ssh', node, cmd]
@@ -67,8 +72,10 @@ def run():
                 run_cmdv(node, cmdv, all, pipedesc)
             else:
                 pendingexecs.append((node, cmdv))
-
-    exitcode = 0
+    if not all:
+        sys.exit(exitcode)
+    if exitcode:
+        sys.exit(exitcode)
     rdy, _, _ = select.select(all, [], [], 10)
     while all:
         for r in rdy: