Add ssh-agent startup when privkey is used

[sreboot]

This change will:

• start ssh-agent when privkey auth is used
• add the key to ssh-agent
• cleanup the agent once the job is over

Useful for scenarios where Rundeck executes a job where further SSH
authentication/connection is required (example: rsync).

[sreboot]

Can someone pls comment on this PR - any issues merging this?

[richiereynolds]

This is a good change but could it be made configurable so that nodes that don't require it don't incur the overheads of using it?
Many jobs use lots of steps which means lots of ssh connections in quick succession and the overheads of each connection soon mount up.
E.g. we found that ssh multiplexing really speeds things up because we're not creating a TCP conenction for each ssh session. It would be bad to slow that down again by starting/stopping ssh-agent prcesses for every session when they might only be needed for very few.
I think the default should be not to use it as my guess is a lot more nodes don't need ssh-agent forwarding than do need it.

[sreboot]

@richiereynolds thanks for the feedback, lemme refactor this with the on/off switch.

[sreboot]

Updated witch checkbox configuration option - default is off.

[sreboot]

@richiereynolds let me know please if this looks OK? Thanks

[sreboot]

@stagrlee @gschueler who is maintaining this repo?

[ltamaster]

Hi @sreboot
Do you have an example (a job) where this feature is used?

Thanks
Luis

[sreboot]

Sorry for the late reply, this is actually not a job specific feature but rather defined as a check-box on the Project level. By default the check-box is not selected.

The agent forwarding can be enabled in the Project settings under the "Default Node Executor" tab as displayed on this screenshot:

If the option is selected it will be picked up by https://github.com/rundeck-plugins/openssh-node-execution/pull/26/files#diff-39297066fbdfdbea1d016e8078109fdb2a74eb98b56291d8532de8fc364637e0R91

Hope this is enough information do describe this change.