[FIX] module: allow disabling 1-click install

As discussed on issue #15225, it should be possible for system administrators
to disable the 1-click installation system.
The plan is to disable the feature by default, but make it relatively easy
to turn on when it is explicitly desired.

1. At the moment we cannot guarantee that all Apps published on the Odoo Apps
   Store are safe. And it is a security risk to let end-users deploy Python
   code on their Odoo servers without requiring any review/deployment by a
   competent system administrator.
   We will work on improving the validation process of the Store, but this
   will require time, and won't probably be a 100% safe process in any case.
2. The one-click install feature is however really useful to help
   non-technical users install Apps, as long as the feature has been
   explicitly allowed by the system administrator. This is a common feature
   in other software suites as well. So we'd like to keep it as an opt-in
   feature.
3. Administrators of multi-tenant servers, cloud hosting services, etc.
   understandably expect to be able to turn off the feature for
   security/control reasons.
4. By turning off the feature by default, but still exposing it in the UI,
   we keep it *discoverable* for users. The error message should be
   helpful to direct users to their sysadmins.
5. By using the permissions of the download folder as a flag for turning
   off the feature, we avoid introducing an extra server parameter.
   The folder is still created (read-only) by default, for the sole purpose
   of making it easier to locate.

Fixes #15225

openerp/addons/base/module/module.py

@@ -659,6 +659,15 @@ class module(osv.osv):
         if not self.pool['res.users'].has_group(cr, uid, 'base.group_system'):
             raise openerp.exceptions.AccessDenied()
 
+        # One-click install is opt-in - cfr Issue #15225
+        ad_dir = openerp.tools.config.addons_data_dir
+        if not os.access(ad_dir, os.W_OK):
+            msg = (_("Automatic install of downloaded Apps is currently disabled.") + "\n\n" +
+                   _("To enable it, make sure this directory exists and is writable on the server:") +
+                   "\n%s" % ad_dir)
+            _logger.warning(msg)
+            raise openerp.exceptions.AccessError(msg)
+
         apps_server = urlparse.urlparse(self.get_apps_server(cr, uid, context=context))
 
         OPENERP = openerp.release.product_name.lower()

openerp/modules/module.py

@@ -94,7 +94,7 @@ def initialize_sys_path():
     global hooked
 
     dd = tools.config.addons_data_dir
-    if dd not in ad_paths:
+    if os.access(dd, os.R_OK) and dd not in ad_paths:
         ad_paths.append(dd)
 
     for ad in tools.config['addons_path'].split(','):

openerp/tools/config.py

@@ -686,10 +686,11 @@ class configmanager(object):
     def addons_data_dir(self):
         d = os.path.join(self['data_dir'], 'addons', release.series)
         if not os.path.exists(d):
-            os.makedirs(d, 0700)
-        else:
-            assert os.access(d, os.W_OK), \
-                "%s: directory is not writable" % d
+            try:
+                # try to make +rx placeholder dir, will need manual +w to activate it
+                os.makedirs(d, 0500)
+            except OSError:
+                logging.getLogger(__name__).debug('Failed to create addons data dir %s', d)
         return d
 
     @property