authentication: remote functionality

[oliver-sanders]

Follow on to #3359
Best attempted after #3445, #3449

Quick fix to re-instate remote functionality:

• Ensure only relevent keys are coppied to remote hosts.
  • Server public
  • Client private
• Perform any modifications to the code required to allow auth to function with just these keys.
• As a temporary measure (until authentication: generate client keys on remote platforms #3443) we can allow private keys to travel.

This work is complete when the remote tests pass:

$ git grep --name-only set_test_remote

[oliver-sanders]

Note: We consider this to be high priority so we can reinstate remote functionality before breakages creep in. This is also a blocker to rose suite-run migration which is due to begin shortly.

[dwsutherland]

Please put this on hold until #3389 is merged, because the network code has been refactored (due to the new PUB/SUB pattern using the same security/logic).

[hjoliver]

(#3389 is merged)