[FIX] base: cherry-pick 55fa0912 to 8.0

Backported to 8.0 following report at #12648

[FIX] base: use datetime instead of date

The variable `date` is compared to the field `name` in the selection
query. `name` is filled in with datetime data. In particular, in the
module currency_rate_live, datetime.now() is used in the name. It is
necessary to make an appropriate comparison to make sure we select the
updated rate right away.

Fixes #12648

openerp/addons/base/res/res_currency.py

@@ -44,7 +44,7 @@ class res_currency(osv.osv):
             context = {}
         res = {}
 
-        date = context.get('date') or time.strftime('%Y-%m-%d')
+        date = context.get('date') or fields2.Datetime.now()
         for id in ids:
             cr.execute('SELECT rate FROM res_currency_rate '
                        'WHERE currency_id = %s '