RabbitMQ 3.1 does not support -p arg for list_channels

Plugin failed for me, but this morning I noticed the error logs to find that newer RabbitMQ 3.1 does not support -p. So, we list channels with vhosts and grep for our $VHOST and apply sed to do the magic :)

Signed-off-by: Rohit Yadav <rohit.yadav@wingify.com>