LU-11400 flr: add 'nosync' flag for FLR mirrors

LU-11400 flr: add 'nosync' flag for FLR mirrors

This patch allows 'nosync' flag to be set for FLR mirror components,
which makes lfs mirror resync skip on mirrors with this flag unless
mirror resync explicitly requested those mirrors to be resync.

This flag can be cleared by set '^nosync' on any component of the
mirror.

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: I209ad91fd9a96d82f8c83a3eb047f665ef4ccf86
Reviewed-on: https://review.whamcloud.com/33205
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>