vl method should return public key (Version: 1.5.0)

[mDuo13]

Summary

The recently-added /vl/{pubkey} method (#3072) should include a public_key field in the response to be consistent with vl.ripple.com.

Motivation

It would be nice if the vl method were exactly comparable to the format served from vl.ripple.com, for two reasons:

• Consistency makes things easier to understand.
• If someone needed to publish their own validator list, they could use a rippled server with a valid TLS key, or pool thereof, to publish the validator list. This reduces the amount of unique infrastructure strictly necessary to run the network.

Solution

When you use the /vl/ method of a rippled server, the resulting JSON object should have the exact same fields as vl.ripple.com. The only difference, currently, is the public_key field, which is known from the request URL but not copied back in rippled's response.