MCO-475 Reraise uncaught exceptions in the receiver_thread to the main thread

If an uncaught exception happens in the body of the reciever_thread
it simply exits unlogged.  With this commit we catch exceptions
raised in this thread and reraise them in the main thread (unless
we're pausing, as we just killed the thread and don't want it
shooting back)
Merge pull request #243 from richardc/MCO-475-runner_exceptions

MCO-475 Reraise uncaught exceptions in the receiver_thread to the main t...
Revert "MCO-456 expose target collective to discovery plugins"

This reverts commit c7d38b54916f2469d9c973bbabc30ae078c0a6bb.

In acceptance testing I see that this is breaking the unfiltered use-case as
Util.empty_filter? fails when the filter contains a collective.  Will propose a
more robust version.
MCO-473 Handle exceptions in securityprovider.decodemsg

Here we add an unverified version of the senders identity.  It's used in one
codepath, that of handling a failure to decode and get at the true sender of a
message.

We also add variant handling of the exception.  If we can be assumed to be a
client (type == :request) then log and press on, otherwise reraise as the
server codepath copes fine.