gce_ssh_addkeys(instance, key.pub = NULL, key.private = NULL, username = Sys.info()[["user"]], overwrite = FALSE)$HOME/.ssh/google_compute_engine.pub or use a different username than
your local username as found in Sys.info[["user"]], otherwise it will configure
itself automatically the first time you use gce_ssh in an R session.If key.pub is NULL then will look for default Google credentials at
file.path(Sys.getenv("HOME"), ".ssh", "google_compute_engine.pub")