Update for usage with solr5

[rfrail3]

This script can be used in solr5 without problem. I just remove the v.4 references and test it. Thanks,

[averni]

Thank you for the contribution, I agree about your observation. Originally the plugin was named just solr but I had to change name since it belongs to another plugin in munin contrib and this script is distributed there too.
On the next pull request I can try to propose a refactoring of the solr folder to the contrib mantainers since this is the only plugin in contrib that works for versions >=4 and the plugin named solr works only for versions <=3 (2012).