FileStore: make _clone() copy spill out marker

Previously we were not doing so, and that resulted in unpredictable loss
of xattrs from the client's perspective.

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
Reviewed-by: Greg Farnum <greg@inktank.com>
(cherry picked from commit 239476a92849159d2a8966d90ca055c116bee91e)
FileStore: set XATTR_NO_SPILL_OUT when creating new files.

Fixes: #8205
Backport: firefly

Signed-off-by: Greg Farnum <greg@inktank.com>
(cherry picked from commit e3b995e1567f3ccc6d00ae27ab2aa99ca157228a)