Modify UDS server startup to set permissions for sockets

Modify UDS server startup to set permissions for sockets

When opening domain sockets for communication, the Haskell daemons did
not set any permissions for the sockets, defaulting to 0700. This was
fine when all of them ran as root, but was bound to cause trouble in a
split-user setup. The first issue is RAPI access after master-failover,
where RAPI could not send make any inquiries until the watcher restored
the desired permissions of the socket.

This patch modifies Luxid to use a g+rw socket, and leaves other servers
to their default of 0600.

Signed-off-by: Hrvoje Ribicic <riba@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>