Extra debug log data to assist finding misbehaving nodes

[nickwales]

We had an issue where a node was making a huge number of session requests resulting in performance issues on the server cluster.

This time we could work out from the requests which node was making the calls however in a situation where that is not obvious having the node name which is creating the request in the debug log would be extremely useful.

Right now a request entry looks like:

2015/10/13 21:36:20 [DEBUG] http: Request /v1/kv/vault-prod-1/core/lock?index=61722103&wait=15000ms (15.514288777s)

Adding node info like this would be my recommendation:

2015/10/13 21:36:20 [DEBUG] [<node_name>] http: Request /v1/kv/vault-prod-1/core/lock?index=61722103&wait=15000ms (15.514288777s)

[slackpad]

Fixed via #1448.