[FIX] auth_signup: portal user redirect to /web after signup

To reproduce:
0. Start an odoo v10 instance with --load=saas_worker,web
1. Install ecommerce.
2. Enable "Allow external users to sign up" and "Enable password
reset from Login page" from General Settings.
3. Open different session then signup a new user.
4. After successfull signup, the new user will be redirected
to the backend (/web).

Facts to consider:
1. odoo.addons.auth_signup.controllers.main.AuthSignupHome and
odoo.addons.website.controllers.main.Website both inherit
odoo.addons.web.controllers.main.Home
2. When instantiating an odoo instance *without* saas_worker,web,
the mro is the following:

( <class 'odoo.http.Home (extended by Website, AuthSignupHome)'>
, <class 'odoo.addons.auth_signup.controllers.main.AuthSignupHome'>
, <class 'odoo.addons.website.controllers.main.Website'>
, <class 'odoo.addons.web.controllers.main.Home'>
, <class 'odoo.http.Controller'>
, <type 'object'>
)

while the mro *with* saas_worker,web loaded is:

( <class 'odoo.http.Home (extended by AuthSignupHome, Website)'>
, <class 'odoo.addons.website.controllers.main.Website'>
, <class 'odoo.addons.auth_signup.controllers.main.AuthSignupHome'>
, <class 'odoo.addons.web.controllers.main.Home'>
, <class 'odoo.http.Controller'>
, <type 'object'>
)

You can notice that depending on how the instance is instantiated,
the order of inheritance is different.

The problem occurs when saas_worker is loaded, so this bug can be
experienced by saas clients.

Explanation of the fix:
Notice that the original code calls web_login of its super in its
web_auth_signup method. This is technique is used normally during
optimization (according to RCO). If website is installed, the
portal user should be redirected to '/' instead of '/web' and this
is defined in web_login of website. However, the web_login of
"website" is not called after signup because "website" is not super
of "auth_signup" when saas_worker is loaded (see the mro above).

Calling self.web_login will make sure that web_login is called from
top to bottom, and regardless of the order of website and auth_signup,
web_login of "website" will be called and makes sure that the
new portal user is redirected to the '/' and not to '/web'.

opw-1956980

closes odoo/odoo#32741

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/auth_signup/controllers/main.py

@@ -32,7 +32,7 @@ class AuthSignupHome(Home):
         if 'error' not in qcontext and request.httprequest.method == 'POST':
             try:
                 self.do_signup(qcontext)
-                return super(AuthSignupHome, self).web_login(*args, **kw)
+                return self.web_login(*args, **kw)
             except (SignupError, AssertionError), e:
                 if request.env["res.users"].sudo().search([("login", "=", qcontext.get("login"))]):
                     qcontext["error"] = _("Another user is already registered using this email address.")
@@ -53,7 +53,7 @@ class AuthSignupHome(Home):
             try:
                 if qcontext.get('token'):
                     self.do_signup(qcontext)
-                    return super(AuthSignupHome, self).web_login(*args, **kw)
+                    return self.web_login(*args, **kw)
                 else:
                     login = qcontext.get('login')
                     assert login, "No login provided."