LU-1203 mdt: map old params to new ones by using an array

LU-1203 mdt: map old params to new ones by using an array

This patch improves mdt_process_config() to use an array for
mapping old params to new ones.

The patch also adds a common function class_find_old_param()
to check whether a proc param is an old one or not, and return
new one if it's an old one.

Signed-off-by: Yu Jian <yujian@whamcloud.com>
Change-Id: If7a79cfa20c7cb57246f115b4af71ff996b77d8d
Reviewed-on: http://review.whamcloud.com/3900
Tested-by: Hudson
Reviewed-by: Liang Zhen <liang@whamcloud.com>
Reviewed-by: Niu Yawei <niu@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>