gss_krb5: prepare for new context format

Prepare for new context format by splitting out the old "v1"
context processing function

Signed-off-by: Kevin Coffman <kwc@citi.umich.edu>
Signed-off-by: Steve Dickson <steved@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>