You can now turn on and off the lease behavior in the generic backend by
using one of two factories. Core uses the normal one if it's not already
set, so unit tests can use the custom one and all stay working.
This also adds logic into core to check, when the response is coming
from a generic backend, whether that backend has leases enabled. This
adds some slight overhead.
/cc @armon - This is a reasonably major refactor that I think cleans up
a lot of the logic with secrets in responses. The reason for the
refactor is that while implementing Renew/Revoke in logical/framework I
found the existing API to be really awkward to work with.
Primarily, we needed a way to send down internal data for Vault core to
store since not all the data you need to revoke a key is always sent
down to the user (for example the user than AWS key belongs to).
At first, I was doing this manually in logical/framework with
req.Storage, but this is going to be such a common event that I think
its something core should assist with. Additionally, I think the added
context for secrets will be useful in the future when we have a Vault
API for returning orphaned out keys: we can also return the internal
data that might help an operator.
So this leads me to this refactor. I've removed most of the fields in
`logical.Response` and replaced it with a single `*Secret` pointer. If
this is non-nil, then the response represents a secret. The Secret
struct encapsulates all the lease info and such.
It also has some fields on it that are only populated at _request_ time
for Revoke/Renew operations. There is precedent for this sort of
behavior in the Go stdlib where http.Request/http.Response have fields
that differ based on client/server. I copied this style.
All core unit tests pass. The APIs fail for obvious reasons but I'll fix
that up in the next commit.
