MB-37187: Rethrow a more useful exception in dcp_replicator runloop
MB-37187: Rethrow a more useful exception in dcp_replicator runloop

Currently if we catch an exception in the dcp_replicator runloop then
we will rethrow it if it was not expected. When we do so we lose both
the exception type and message and rethrow an empty std::exception.

Rethrow a runtime_error exception instead with the message of the
original exception to at least preserve the exception message.

Change-Id: I596dc1c1332fefe7d64b0b7167bf8945a00cd6aa
Reviewed-on: http://review.couchbase.org/119417
Well-Formed: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine