Ensure Agent ID creation is idempotent.

The Opsmatic Agent ID creation only happened once due
to the 'refreshonly' tag. This removes that, and re-executes
the creation appropriately if any of the /identity/ files
are found to be missing.

Additionally, do not even create the Exec[] resource if
we're not installing the service, otherwise it will fail
during the uninstall of the service.
Bugfix: Don't require a resource that might not exist if  => absent.
Bugfix: Add explicit path to Exec[] statement.
Lint
Merge pull request #6 from Nextdoor/regenerate_client_keys

Regenerate client keys