Move create_rhizome_identities() from testdefs_rhizome.sh to
create_identities() in testdefs.sh
Rename create_identity() in testdefs.sh to create_single_identity(), uses
create_identities() to do its work.
Servald starts DNA helper, receives startup ACK, sends requests, receives
responses, handles malformed helper responses, echoes dnahelper stderr lines to
log, sends MDP reply packet, waits for dead helper process, all asynchronously.
Shuts down helper process during servald shutdown.
Remaining issues:
- Does not impose a timeout on helper responses.
- Only the first URI is reported by the "dna lookup" command.
... as part of working on work on DNA helper callout facility.
(DNA replies now contain a token that can be used to match them
against DNA requests as a happy side-effect).
