[IMP] sql_db: Improve error message logging on database querries

Purpose:

When we have a SQL error, it's not very easy to identify the root of the crash. For example if a mandatory field is not set on a row creation, it difficult to see which field isn't correctly set as a lot of fields are not required and a lot a NULL values are present in the INSERT querry.

Specification:

Show a proper log message, with the reason (cause) of the sql error.

Behavior Modification Examples:
Some sample log after applied fix. The new line are those beginning by '+'

2016-10-25 09:59:40,208 21161 INFO ent_master odoo.sql_db: bad query: INSERT INTO "res_partner_category" ("id", "active", "color", "create_uid", "write_uid", "create_date", "write_date") VALUES(nextval('res_partner_category_id_seq'), true, 10, 1, 1, (now() at time zone 'UTC'), (now() at time zone 'UTC')) RETURNING id
+REASON: null value in column "name" violates not-null constraint
+DETAIL:  Failing row contains (27, null, null, 1, null, 10, 1, null, 2016-10-25 09:59:40.207202, t, 2016-10-25 09:59:40.207202).

2016-10-25 10:00:29,710 21161 INFO ent_master odoo.sql_db: bad query: UPDATE "res_partner" SET "parent_id"=1001,"type"='contact',"name"='Course Script',"company_name"=NULL,"write_uid"=1,"write_date"=(now() at time zone 'UTC') WHERE id IN (1)
+REASON: insert or update on table "res_partner" violates foreign key constraint "res_partner_parent_id_fkey"
+DETAIL:  Key (parent_id)=(1001) is not present in table "res_partner".

2016-10-25 10:23:28,690 21336 INFO ent_master odoo.sql_db: bad query: DELETE FROM res_country WHERE id IN (235)
+REASON: null value in column "country_id" violates not-null constraint
+DETAIL:  Failing row contains (9, 1, AL, Alabama, null, 1, 2016-10-24 10:19:58.765552, 2016-10-21 09:32:26.939607).
+CONTEXT:  SQL statement "UPDATE ONLY "public"."res_country_state" SET "country_id" = NULL WHERE $1 OPERATOR(pg_catalog.=) "country_id""

1 files changed, 2 insertions, 2 deletions

diff --git a/odoo/sql_db.py b/odoo/sql_db.py
index f2b200225a2..a7c7d6fc54d 100644
--- a/odoo/sql_db.py
+++ b/odoo/sql_db.py
@@ -216,9 +216,9 @@ class Cursor(object):
         try:
             params = params or None
             res = self._obj.execute(query, params)
-        except Exception:
+        except Exception as e:
             if self._default_log_exceptions if log_exceptions is None else log_exceptions:
-                _logger.info("bad query: %s", self._obj.query or query)
+                _logger.info("bad query: %s \nERROR: %s", self._obj.query or query, e)
             raise
 
         # simple query count is always computed