LOGSTASH-1886: intercept exception raised by march_hare

Since ae867bc64, the march_hare version we use raises an error when the
network link is broken while the socket is idle. This case must be
handled by logstash to initiate the reconnection process.
Merge pull request #1665 from mfournier/LOGSTASH-1886-2nd_try

LOGSTASH-1886: intercept exception raised by march_hare