LU-4933 osc: Automatically increase the max_dirty_mb

LU-4933 osc: Automatically increase the max_dirty_mb

When RPC size or the max RPCs in flight is increased, the actual
limit might be max_dirty_mb. This patch automatically increases
the max_dirty_mb value at connection time and when the related
values are tuned manually by proc file system.

this patch also changes the unit of "cl_dirty" and "cl_dirty_max"
in client_obd from byte to page.

Change-Id: Ieaea7660caa8008365b38f548b4ecba4027e080b
Signed-off-by: Li Xi <lixi@ddn.com>
Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-on: http://review.whamcloud.com/10446
Tested-by: Jenkins
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>