[FIX] undefined variable

Variable was added to an error message, then inlined in only one of the
two callsites. Undefined variable error would only appear when an error
is triggered in the actual (postgres-level) backup call.

inserted in ec9a543

fixes odoo#5241

openerp/tools/misc.py

@@ -122,7 +122,8 @@ def exec_pg_command(name, *args):
     prog = find_pg_tool(name)
     env = exec_pg_environ()
     with open(os.devnull) as dn:
-        rc = subprocess.call((prog,) + args, env=env, stdout=dn, stderr=subprocess.STDOUT)
+        args2 = (prog,) + args
+        rc = subprocess.call(args2, env=env, stdout=dn, stderr=subprocess.STDOUT)
         if rc:
             raise Exception('Postgres subprocess %s error %s' % (args2, rc))