Install handler if enabled

This patch install handler only if enabled is not defined or set to
True.

Change-Id: I63b0d1a06f4de072c758f56ccccffdfcb197bcf6
diff --git a/sensu/server.sls b/sensu/server.sls
index 4882acf..2e38e9f 100644
--- a/sensu/server.sls
+++ b/sensu/server.sls
@@ -86,7 +86,7 @@
 
 {%- for handler_name, handler in server.get('handler', {}).iteritems() %}
 
-{%- if handler_name in ['default', 'flapjack', 'mail', 'sccd', 'stdout', 'statsd', 'slack', 'pipe', 'sfdc', 'pagerduty', 'hipchat']  %}
+{%- if handler.get('enabled', True) and handler_name in ['default', 'flapjack', 'mail', 'sccd', 'stdout', 'statsd', 'slack', 'pipe', 'sfdc', 'pagerduty', 'hipchat'] %}
 
 {%- include "sensu/server/_handler_"+handler_name+".sls" %}