New functional-ssh-keys test is non-voting

[Martin Packman]

The new functional-ssh-keys test is non-voting while it gathers a few
runs and awaits a branch landing.

<http://juju-ci.vapour.ws/job/functional-ssh-keys/>

The test was written as part of fixing lp:1555727 as we lacked
functional test coverage for the key management in juju, and with some
pending updates works against 1.25 as well as master.

Martin