ceph: properly handle XATTR_CREATE and XATTR_REPLACE

return -EEXIST if XATTR_CREATE is set and xattr alread exists.
return -ENODATA if XATTR_REPLACE is set but xattr does not exist.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
ceph: remove zero-size xattr

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
ceph: ceph_removexattr()

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
ceph: add missing init_acl() for mkdir() and atomic_open()

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
ceph: fix ceph_set_acl()

If acl is equivalent to file mode permission bits, ceph_set_acl()
needs to remove any existing acl xattr. Use __ceph_setxattr() to
handle both setting and removing acl xattr cases, it doesn't return
-ENODATA when there is no acl xattr.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>