[Feature] - Add HostId values for REST XML error responses

[lrm25]

Describe the solution you'd like Error responses coming directly from S3 have a format similar to the following:

<?xml version="1.0" encoding="UTF-8"?>
<Error><Code>MissingRequestBodyError</Code><Message>Request Body is empty</Message><RequestId>QD651ANCQX2QXBWR</RequestId><HostId>1U0g3tI0BtEqJNbi0pg2wgtSjhIK2h+YGWDjTDiMiLHGhHxydxZlU3L/B9aohbXWxMdlk+lEkF+36yeDzfBaMaxNAPH8L6XP</HostId></Error>

Via versitygw, the RequestId and HostId are both empty. RequestId can remain empty, since there are currently not any plans to implement it, but adding the HostId may be useful for load balancing setups.