Add slice expiration and renewal to the CH; SA will reregister slices when they are renewed and the CH updates the expiration.
Add slice expiration and renewal to the CH; SA will reregister slices
when they are renewed and the CH updates the expiration.

Add a note that Shutdown needs to take a slice credential, not a
clearinghouse credential. Accept both for now, until new SA makes it
out to everyone.

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome