loom.tasks.ssh doesn't work with multilple env.key_filenames

[sherzberg]

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Fabric allows you to set env.key_filename to be a list of keys and the ssh task in loom doesnt work when you have multiple keys defined.

[bfirsh]

Half fixed in 374f9263a3b6ae82aca7b81ec00622bf50999399 where it'll use the first key in the list.