When using gnt-cluster master-failover, on the soon-to-be-master the
luxi daemon is started by the node daemon. This makes the luxi
daemon inherit the node daemon's umask 077, making the communication
socket unreadable to group members. When using Ganeti with non-root
users, this causes problems, as reported in issue 477.

To fix this, the socket permissions are set explicitly.

Signed-off-by: Hrvoje Ribicic <riba@google.com>
Reviewed-by: Michele Tartara <mtartara@google.com>