Fix prepared statement reconnect issue

This commit fixes an issue where, if the connection between Logstash
and the database fails due to an attempt to use a closed prepared statement.
This results in subsequent attempts to use a prepared statement
failing when using scheduling, which can only be rectified by restarting Logstash.

This commit resets the `statement_prepared` flag, which means that the
prepared statement will be recreated upon the next scheduled run.

This commit also adds a backtrace to log entries when this issue occurs to provide
more visibility into the cause of the issue.

lib/logstash/plugin_mixins/jdbc/jdbc.rb

@@ -260,7 +260,9 @@ def execute_statement
         end
         success = true
       rescue Sequel::DatabaseConnectionError, Sequel::DatabaseError, Java::JavaSql::SQLException => e
-        @logger.warn("Exception when executing JDBC query", :exception => e)
+        details = { :exception => e.message }
+        details[:backtrace] = e.backtrace if @logger.debug?
+        @logger.warn("Exception when executing JDBC query", details)
       else
         @value_tracker.set_value(sql_last_value)
       ensure

lib/logstash/plugin_mixins/jdbc/statement_handler.rb

@@ -97,7 +97,14 @@ def build_query(db, sql_last_value)
       end
       bind_value_sql_last_value(sql_last_value)
       statement_logger.log_statement_parameters(statement, parameters, nil)
-      db.call(name, parameters)
+      begin
+        db.call(name, parameters)
+      rescue => e
+        # clear the statement prepared flag - the statement may be closed by this
+        # time.
+        statement_prepared.make_false
+        raise e
+      end
     end
 
     def post_init(plugin)

spec/inputs/integration/integ_spec.rb

@@ -3,7 +3,6 @@
 require "sequel"
 require "sequel/adapters/jdbc"
 
-# This test requires: Firebird installed to Mac OSX, it uses the built-in example database `employee`
 
 describe LogStash::Inputs::Jdbc, :integration => true do
   # This is a necessary change test-wide to guarantee that no local timezone