Database.max_retries only override on sqlalchemy side

Currently, the max_retries parameter will be override in
get_connection_from_config function. But it will be used
later in safe_mongo_call function.

Since the override of max_retries only need on sqlalchemy
side, this patch move the override from get_connection_
from_config to storage.impl_sqlalchemy.Connection.__init__
and make sure max_retries can be used on mongoDB side.

Change-Id: I83f35c886bc8b7299c1efd7297fdbc980214567f
Closes-Bug: #1395972
(cherry picked from commit afb90e0cfc7fadae17ed9d360124e5683cb0b99a)