Deployment with Security Team Permission

Deployment with Security Team Permission

Permitting deployment during embargo seemed to have rough consensus on
the principle.  We seemed to be converging on the idea that the
Security Team should explicitly set deployment restrictions for each
set of patches.

IMPLEMENTATION TASKS:
 * Add new section to Security Team's advisory template.
 * Add new section to any existing outstanding embargoed advisories.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>