fsck.ubifs: Read master node & init lpt

fsck.ubifs: Read master node & init lpt

This is the 1/18 step of fsck. Read and check master node, init lpt.
There could be following errors:
 1. corrupted scanning data in master area or invalid master node:
    danger mode with rebuild_fs and normal mode with 'yes' answer will
    turn to rebuild filesystem, other modes will exit.
 2. incorrect space statistics in master node: Set %FR_LPT_INCORRECT for
    for lpt status. Ignore the error.
 3. corrupted lpt: Set %FR_LPT_CORRUPTED for lpt status. Ignore the error.

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>