LU-9699 osp: don't assert on OSP duplicating

LU-9699 osp: don't assert on OSP duplicating

Writeconf on an MDT with index > 0000 will cause
"add mdc" to be added to $FSNAME-client config
and "add osp" to be added to $FSNAME-MDTXXXX configs.

However, the configs may already contain these
directives. Duplicating the OSP device will
cause the assertion failure in osp_obd_connect():
	ASSERTION( osp->opd_connects == 1 ) failed

Duplicating the MDC just returns -EEXIST in similar
situation.

A possible solution is to check configs for duplicates
before writing to them. However, sometimes we
would like to change nids which are part of
"add mdc" and "add osp".

Another solution is to mark previous entries with
SKIP flags. This patch implements this approach.
Since after revoking the config lock, the clients
and the MDTs will receive the updated log and
apply its newer entries, we still have to handle
OSP duplication, but this is only an issue
immediately after writeconf processing.

Seagate-bug-id: MRP-2634, MRP-3865
Change-Id: Idd7ad43c78d50e6bbe715850503aa0b01fcbf071
Signed-off-by: Mikhail Pershin <mpershin@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/27753
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Andrew Perepechko <andrew.perepechko@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>