LU-9771 lod: define ldo_mirrors to manage mirrors

LU-9771 lod: define ldo_mirrors to manage mirrors

Right now it only supports loading mirror from disk

Test-Parameters: testlist=sanity-flr
Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Change-Id: Id560070e6147465681ede5a02e1add585281ea89
Reviewed-on: https://review.whamcloud.com/29089
Tested-by: Jenkins
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Tested-by: Maloo <hpdd-maloo@intel.com>