Enable the addition of extra logstash-filters through extra bosh release

This is an BOSH implementation showing how to integrate [additional logstash-filters]( http://labs.cityindex.com/labs-team/2014/03/27/rfc-logstash-filter-repositories/) into an existing `logstash-boshrelease`

In summary, you extend your logsearch deployment manifest like this:

```
releases:
  - name: logsearch
    version: latest
  - name: logsearch-cf_parsers
    version: latest

...

jobs:
- name: log_parser
  release: logsearch
  templates: 
  - name: log_parser
  - name: logstash-filters-cf
    release: logsearch-cf_parsers
```

The `logstash-filters-cf` job places additional logstash filters in `/var/vcap/packages/logstash-filters-cf/logstash-filters-cf.conf`

On installation, the `log_parser` job includes all additional filters from `/var/vcap/packages/logstash-filters-*/logstash-filters-*.conf`