Check authorized keys owner/group/permissions before running chmod/chown

[srstsavage]

Fixes #4

Check /root/.ssh and (if it exists) /root/.ssh/authorized_keys existing owner, group, and permission before attempting to adjust with chown and chmod. This should allow k8s deployments using configmaps and other deployment mechanisms which mount a read only authorized_keys file to successfully run.

Note that the provided authorized_keys file must already have the correct owner (root), group (root), and permissions (400).