Steps to reproduce (on 5.4):

1. Simply install a 5.4, and update it according to the steps provided at:
https://doc.ez.no/display/EZP/5.4.x+Update+Instructions

2. Now fetch and install Solr according to the steps provided at:
https://doc.ez.no/display/EZP/Solr+Search+Engine+Bundle

3. When setting up your solr configuration on ezpublish.yml:

ez_search_engine_solr:
    endpoints:
        endpoint0:
            dsn: %solr_dsn%
            core: collection1
    connections:
        default:
            entry_endpoints:
                - endpoint0
            mapping:
                default: endpoint0
		

The "dsn" value is being fetched from parameters.yml, but on a 5.4 this value is not referred anywhere in that doc page for Solr.
From a customer's perspective, one wouldn't know what to write on parameters.yml or straight in ezpublish.yml.
On a master version though, the value is defined on parameters.yml as:

solr_dsn: 'http://localhost:8983/solr'