LU-15112 mgc: do not ignore target registration failure

LU-15112 mgc: do not ignore target registration failure

A serious target registation failure with LDD_F_ERROR
flag set is ignored by target, it makes possible
registreting new target with already used index;
Writeconf flag should be encoded in fs label regardless
the "first_time" flag, otherwise target cannot be registered
after initial registration failure.

HPE-bug-id: LUS-8752
Signed-off-by: Alexander Zarochentsev <alexander.zarochentsev@hpe.com>
Change-Id: If051199d3dbafc8f8102f3daf086de01bc5c5f98
Reviewed-on: https://review.whamcloud.com/45259
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Alexey Lyashkov <alexey.lyashkov@hpe.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>