rpc/http: Show pending RPC requests in lock monitor

Not all requests use an instance of RpcRunner yet and therefore won't
show up (only instances have access to the global Ganeti context).
Currently only the IP address is accessible. Another patch will add a
nicer name for requests.

Example output (gnt-debug locks -o name,pending):
Name                      Pending
rpc/192.0.2.18/test_delay thread:Jq12/Job683/TEST_DELAY

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>