s3: OneFS unmappable sids support.

s3: OneFS unmappable sids support.

Updates the onefs vfs module to add configurable behavior to deal
with sids that are unknown to us.  The best examples are aces that
come from robocopy/xcopy.

Adds the following share level options (which are specific to the vfs_onefs
module):

onefs: ignore unmappable sids (Default = false)
If this option is set to true, sids which could not be resolved to
a uid/gid are ignored.  If an unmappable sid is encountered as the owner
or group, the owner/group is converted to BUILTIN\Administrators.

onefs: unmappable sids ignore list (Default = empty)
Only the sids in the list are ignored.

onefs: ignore sacls (Default = false)
SACLs are ignored

onefs: unmappable sids deny everyone (Default = false)
If an unmappable sid is found in a deny ACE, the ACE's identity is
changed to Everyone.