avocado.plugins.wrapper: Check the --gdb-run-bin value

--gdb-run-bin is incompatible with --wrapper option. The original code
checked presence of "gdb_run_bin" in args, but it's always present with
default value `[]`. This patch changes the check to gettattr.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

avocado/plugins/wrapper.py

@@ -48,9 +48,10 @@ class Wrapper(CLI):
                                 'only one global wrapper can be defined.')
 
     def run(self, args):
-        if 'wrapper' in args:
+        wraps = getattr(args, "wrapper", None)
+        if wraps:
             view = output.View(app_args=args)
-            if 'gdb_run_bin' in args and args.gdb_run_bin:
+            if getattr(args, 'gdb_run_bin', None):
                 view.notify(event='error',
                             msg='Command line option --wrapper is incompatible'
                                 ' with option --gdb-run-bin.')