Get mysql_sql_mode parameter from config

Patch Ia527e850671ab9542db5864617384cee21e91bf6 added mysql_sql_mode
option to config, so we should get it's value from CONF object, not
from function argument.

Closes-Bug: #1288445

Change-Id: I4be81718399393d817185abe36f4cc4d3da15000
Merge "Get mysql_sql_mode parameter from config"