r13402: Make Samba4 pass a nastier RPC-SCHANNEL test.

r13402: Make Samba4 pass a nastier RPC-SCHANNEL test.

The new RPC-SCHANNEL test shows that the full credentials state must
be kept in some shared memory, for some length of time.  In
particular, clients will reconnect with SCHANNEL (after loosing all
connections) and expect that the credentials chain will remain in the
same place.

To achive this, we do the server-side crypto in a transaction,
including the fetch/store of the shared state.

Andrew Bartlett