MCO-411 remove examples of catching RPCErrors in response blocks

It was originally intended that the appropriate exception for a
given rpc response would be propogated into the block supplied to
the call_agent method.  This isn't possible in ruby as noted in the
discussion around MCO-264.

Here we rework the misleading example code to reflect that we no
longer attempt to re-raise the exception in the supplied block, and
instead demonstrate testing response[:body][:statuscode].
MCO-351 Fix rabbitmq connector under custom discovery

If reply_to is set use it. In the case of using a custom discovery method,
the direct addressing method is used. In this case we want to keep the
reply_to if it is set by the command line.
Merge pull request #212 from richardc/MCO-411_docs_for_MCO-264

MCO-411 remove examples of catching RPCErrors in response blocks
(MCO-93) Introduce the ability to reset limit_targets

This commit adds the ability to RPC::Client#limit_targets= to reset
the @limit_targets instance variable by passing a nil or false value.
Merge pull request #214 from ploubser/mco-93

(MCO-93) Introduce the ability to reset limit_targets
Merge pull request #213 from richardc/finish_pr_198

MCO-351 Fix rabbitmq connector under custom discovery
maint - it's plugin.d, not plugins.d