LU-6952 mount: Mount options parsing problem

LU-6952 mount: Mount options parsing problem

The code which parse the mount option expect that the default
mount options come first and then the user given options. But
actually the default options are appended after the user given
option. Because of this user given options are cleared.
Following code fix this bug.

Added a conf-sanity test 104 to verify this fix.

Seagate-bug-id: MRP-2193
Signed-off-by: Pratik Shinde <pratik.shinde@seagate.com>
Signed-off-by: Rahul Deshmukh <rahul.deshmukh@seagate.com>
Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Change-Id: I1a22e5d559e01d8bcba0ceebba5544e92d39bb19
Reviewed-on: https://review.whamcloud.com/15906
Reviewed-by: Jian Yu <jian.yu@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Grégoire Pichon <gregoire.pichon@bull.net>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>