Make parent-child security session in CEDAR usable. #4405

In order for the pre-created security session between parent and child
daemons to be usable, the child needs to know the list of command
integers that the session can be used with. We now pass that in the
serialized session string passed from parent to child.
The child also needs to include the parent's sinful string in the
session structure it creates from the inherited serialized string.
Children of the schedd now use shadow socket for all commands. #4405

Daemons can now set an alternate sinful string in the CONDOR_INHERIT
environment variable for how a child daemon should contact them.
The schedd uses this to have the daemons it spawns use the shadow
command socket for all communication. Previously, the children would use
the main command port to send CHILDALIVE commands.
Docs for working parent-child security sessions. #4405