"Enter passphrase for key" appears sometimes when key is passed during `disco init` with `-i` but file has no passphrase...!

[gregsadetsky]

repro: generate ed25519 key while creating ec2 machine, pass it to disco init with -i flag - there should be no passphrase ask (as just pressing enter ie not passing a passphrase) works

[gregsadetsky]

poooooooooootentially because private key did not have 600 permissions, and so error code (from command that checks whether passphrase is on) was incorrectly detected as meaning that this key had a passphrase...!!

[gregsadetsky]

definitely because not chmod 600!