DLPX-61319 Cloud-init fails to add authorized user ssh key

[pzakha]

See https://bugs.launchpad.net/cloud-init/+bug/1404060 for the launchpad bug.

On our internal-dev variants, we configure password-less login for DCOA instances by passing the user's ssh key to cloud-init.
Cloud-init normally adds that key to the authorized_keys file for the default (delphix) user, or to the file configured in sshd_config. However, since we have 2 entries for AuthorizedKeysFile in sshd_config instead of one, cloud-init gets confused and parses those 2 entries as a single long file name. As a result, it adds the key to that new file which is not parsed by sshd, and so password-less access doesn't work.

Testing

1. Build cloud-init using the linux-pkg framework, and manually deploy it on an internal-dev system.
2. run sudo cloud-init clean -lr to reboot the system and force cloud-init to re-run.
3. The user key is now added to ~/.ssh/authorized_users and password-less ssh works.

[pzakha]

Verified that a Delphix Appliance built with those changes can be accessed with passwordless ssh.

Built package available here: s3://dev-de-images/builds/jenkins-selfservice.pzakharov/devops-gate/master/linux-pkg-build/master/pre-push/41/cloud-init_18.4-delphix-2018.11.28.16_all.deb
DCOA group: pzakha-ab21-trunk