LU-17317 gss: do not continue using expired reverse context

LU-17317 gss: do not continue using expired reverse context

In case a server uses an expired gss context to send a callback
request to a client, it might be that the associated context on
the client has already expired, and been purged from the cache.
This results in a GSS_S_NO_CONTEXT reply.
In this specific scenario, the server must mark its reverse context
as dead. This will lead to destruction of the expired context, and
creation of a new context suitable for further callback requests.

Test-Parameters: kerberos=true testlist=sanity-krb5
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I4af90cd70a3815851ec555ea85b49714c8da4202