Host is unable to use keys from ssh-agent while provisioning

[ajsalminen]

Vagrant 1.9.5 seems to fail using the default insecure key at all when "config.ssh.keys_only = false" is set. Setting the private key manually causes IdentitiesOnly to be always set for ssh. This means we can't use any other keys and things like mysql_sync fail during the provisioning.

Seems like there are upcoming changes to the code handling this in vagrant so maybe it will be fixed in a future release. If all else fails, config.ssh.extra_args could be used to circumvent this once it's available.