Bug fix: Don't look for VAULT_ADDR if the vault plugin is not configured
Bug fix: Don't look for VAULT_ADDR if the vault plugin is not configured

When the Vault plugin gets called as a generator, it's not fully
configured, and so it shouldn't try to connect to vault.

I'm not sure it was a bright idea to put generators and transforms in
the same plugins.  Oh well.

faradayio/cage,faradayio/cage