fsx: add support for recording operations to a file

fsx: add support for recording operations to a file

Usually, fsx dumps an .fsxops file on failure with same basename
as work file and possibly under dirctory specified by -P dirpath.

The --record-ops[=opsfile] flag can be use to dump ops file also
on success and to optionally specify the ops file name.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>