semanage: Print usage when no args

https://bugs.python.org/issue16308

Traceback (most recent call last):
  File "semanage", line 932, in <module>
    do_parser()
  File "semanage", line 911, in do_parser
    args.func(args)
AttributeError: 'Namespace' object has no attribute 'func'

Signed-off-by: James Carter <jwcart2@tycho.nsa.gov>

policycoreutils/semanage/semanage

@@ -856,6 +856,7 @@ def createCommandParser():
 
     #To add a new subcommand define the parser for it in a function above and call it here.
     subparsers = commandParser.add_subparsers(dest='subcommand')
+    subparsers.required = True
     setupImportParser(subparsers)
     setupExportParser(subparsers)
     setupLoginParser(subparsers)