Use standard functions for parsing/validating email addresses.

This adds two new functions for parsing out the domain and username
from an email address, and switches our backend to use them and
django.core.validators.valid_email() rather than custom parsing and
raw email.split("@").

(imported from commit 3d6e997d66908811eccb5f82f2f7fe349b40f238)

zephyr/management/commands/create_user.py

@@ -8,7 +8,7 @@ from django.core.exceptions import ValidationError
 from django.db.utils import IntegrityError
 from django.core import validators
 
-from zephyr.models import Realm
+from zephyr.models import Realm, email_to_username
 from zephyr.lib.actions import do_create_user
 from zephyr.views import notify_new_user
 from zephyr.lib.initial_password import initial_password
@@ -67,7 +67,7 @@ parameters, or specify no parameters for interactive user creation.""")
 
         try:
             notify_new_user(do_create_user(email, initial_password(email),
-                realm, full_name, email.split('@')[0]),
+                realm, full_name, email_to_username(email)),
                 internal=True)
         except IntegrityError:
             raise CommandError("User already exists.")