Fix exit code for command line errors

Fixes #3913

src/_pytest/config/argparsing.py

@@ -2,8 +2,13 @@ import six
 import warnings
 import argparse
 
+from gettext import gettext as _
+import sys as _sys
+
 import py
 
+from ..main import EXIT_USAGEERROR
+
 FILE_OR_DIR = "file_or_dir"
 
 
@@ -329,6 +334,16 @@ class MyOptionParser(argparse.ArgumentParser):
         # an usage error to provide more contextual information to the user
         self.extra_info = extra_info
 
+    def error(self, message):
+        """error(message: string)
+
+        Prints a usage message incorporating the message to stderr and
+        exits.
+        Overrides the method in parent class to change exit code"""
+        self.print_usage(_sys.stderr)
+        args = {"prog": self.prog, "message": message}
+        self.exit(EXIT_USAGEERROR, _("%(prog)s: error: %(message)s\n") % args)
+
     def parse_args(self, args=None, namespace=None):
         """allow splitting of positional arguments"""
         args, argv = self.parse_known_args(args, namespace)