Move event listener out of server callback.
Move event listener out of server callback.

Without this change, an event listener was being added
for each request and node was providing a memory leak
warning in the server logs after only a handful of requests.

tomateos/S3,lucisilv/Silviu_S3-Antidote,tomateos/S3,scality/S3,scality/S3,truststamp/S3,truststamp/S3,tomateos/S3,lucisilv/Silviu_S3-Antidote,truststamp/S3,truststamp/S3,truststamp/S3,scality/S3,truststamp/S3,truststamp/S3,lucisilv/Silviu_S3-Antidote,scality/S3,scality/S3,tomateos/S3,scality/S3,lucisilv/Silviu_S3-Antidote,lucisilv/Silviu_S3-Antidote,tomateos/S3,truststamp/S3,scality/S3,lucisilv/Silviu_S3-Antidote,lucisilv/Silviu_S3-Antidote,tomateos/S3,tomateos/S3,scality/S3,tomateos/S3,lucisilv/Silviu_S3-Antidote