Monit to check Solr status via its API

It should be possible to extend Monit configuration for Solr by adding an HTTP query. A HTTP response other than 200 _should_ mean it's down, although processing the output will be nicer :)

```
Solr-test-host ~ # curl "http://localhost:8983/solr/admin/ping?wt=json&indent=on"
{
"responseHeader":{
"status":0,
"QTime":3,
"params":{
"q":"solrpingquery",
"indent":"on",
"wt":"json",
"echoParams":"all",
"distrib":"false",
"df":"text",
"rows":"10"}},
"status":"OK"}
Solr-test-host ~ #
```