Merge pull request #2434 from ltalirz/issue_2355_verdi_help_exit_status

let verdi help return exit status 0

Author: yakutovicha

aiida/cmdline/verdilib.py

@@ -294,7 +294,7 @@ def run(self, *args):
             print ""
             print ("Use '{} help <command>' for more information "
                    "on a specific command.".format(execname))
-            sys.exit(1)
+            sys.exit(0)
 
         if command in short_doc:
             print "Description for '%s %s'" % (execname, command)