Add solr core 'test' to the testing machine

[HirschSt]

For testing purposes rspec really should have it's own solr core (and not share the same core with production :-) ), see:

https://github.com/rism-digital/muscat/blob/bce5713176865d42ec8225f106c0f3e75d0bc705/config/sunspot.yml#L26