RFR: Fix: Sensu handler trigger type registration

```
vagrant@st2express:~$ cat sensu.json | /tmp/st2_handler.py
POST: url: http://localhost:6000/webhooks/st2/, body: {'name': 'sensu.event_handler', 'payload': {'action': 'create', 'client': {'timestamp': 1326390159, 'subscriptions': ['all', 'frontend', 'proxy'], 'name': 'host01', 'address': '10.2.1.11'}, 'check': {'status': 2, 'name': 'frontend_http_check', 'issued': 1326390169, 'interval': 60, 'handler': 'campfire', 'command': "check_http -I 127.0.0.1 -u http://web.example.com/healthcheck.html -R 'pageok'", 'flapping': False, 'subscribers': ['frontend'], 'output': 'HTTP CRITICAL: HTTP/1.1 503 Service Temporarily Unavailable', 'history': ['0', '2']}, 'occurrences': 1}}
Sent sensu event to st2. HTTP_CODE: 202
vagrant@st2express:~$
```
I just checked and it looks like webhook schema still hasn't been updated so it expects a name (`./st2reactor/st2reactor/contrib/sensors/st2webhookschemas/st2webhooks.json`).

Good catch.

Anyways, the webhook schema and the webhook handler need to be updated to take just a `type` (reference to a trigger type) instead of `name` + `type` which is what it currently expects.