We have run into a case where we need to store a secret longer
than 3760 bits. We may eventually support a hybrid encryption
scheme, but for now, let's also support the alt.zuul.secrets protocol
where we split the secret into 3760 bit chunks and recombine it.
The encrypt_secret utility is updated to output a copy-pastable
YAML data structure to simplify dealing with long secrets.
Change-Id: Ied372572e5aa29fddfb7043bf07df4cd3e39566c
9118c01ecf