solr.cfg: configure JMX host and port separately.

[mauritsvanrees]

The config was hardcoding the JMX (Java Management Extensions) host and port. Now it is clearer that you can configure them.

Mostly, I found it strange that there was a solr-port setting and we were completely ignoring that in the java_opts and instead used hardcoded port 8984. To me this gave the impression that this port 8984 was only used at build time to maybe set a default, and that solr-instance fg would just use the port from the settings and port 8984 would never be used.

Initially I changed that to use the same settings, with ${:host} and ${:port}.
That seems to work fine, and we could also use that to keep things simple.
But probably it is better to keep the ports separate.

I did not know JMX, but you can start jconsole and connect to your Solr instance and see some statistics. See https://cwiki.apache.org/confluence/display/solr/Using+JMX+with+Solr

[gforcada]

When running multiple jenkins jobs one can lead to a situation where both jobs try to bind to that port, so getting a random port from jenkins port allocator for both connections will be really helpful.

[tisto]

@mauritsvanrees pls fix merge conflicts.

[mauritsvanrees]

I have rebased.

[mauritsvanrees]

BTW, I think this is my last fix for collective.solr (and one pull request pending for the solrinstance recipe) for the short future, so releases are welcome. :-)

[tisto]

@mauritsvanrees will do a release soon.