astakos: Respect module specific policies

also disable switch policy of shibboleth and local providers by default.
In the case of local provider it just doesn't make sense. Shibboleth doesn't
allow us to create a url which would force user to login with different
credentials.

snf-astakos-app/astakos/im/auth_providers.py

@@ -173,6 +173,8 @@ class AuthProvider(object):
             setting_key = "%s_POLICY" % policy.upper()
             if self.has_setting(setting_key):
                 self.module_policies[policy] = self.get_setting(setting_key)
+            else:
+                self.module_policies[policy] = value
 
         # messages cache
         self.message_tpls_compiled = OrderedDict()
@@ -553,7 +555,8 @@ class LocalAuthProvider(AuthProvider):
     }
 
     policies = {
-        'limit': 1
+        'limit': 1,
+        'switch': False
     }
 
     @property
@@ -582,6 +585,10 @@ class ShibbolethAuthProvider(AuthProvider):
     login_view = 'astakos.im.views.target.shibboleth.login'
     username_key = 'identifier'
 
+    policies = {
+        'switch': False
+    }
+
     messages = {
         'title': _('Academic'),
         'login_description': _('If you are a student, professor or researcher'