Gracefully handle all exceptions

We detect Riemann communication errors and in such circumstances, drop
events and continue processing operations in order to cope with
transient communication failures.

Some network errors raise generic SocketError exceptions,
OpenSSL::SSL::SSLError or EOFError exceptions.  Such errors should
likewise also be ignored instead of causing the program termination.

lib/riemann/tools/riemann_client_wrapper.rb

@@ -25,11 +25,8 @@ def initialize(options)
             events << @queue.pop while !@queue.empty? && events.size < @max_bulk_size
 
             client.bulk_send(events)
-          rescue Riemann::Client::Error => e
-            warn "Dropping #{events.size} event#{'s' if events.size > 1} due to #{e}"
           rescue StandardError => e
-            warn "#{e.class} #{e}\n#{e.backtrace.join "\n"}"
-            Thread.main.terminate
+            warn "Dropping #{events.size} event#{'s' if events.size > 1} due to #{e}"
           end
         end