Download directory and temporary directory should be distinct

[frgomes]

Imagine a scenario where you provide all binary archives and other external resources on a read-only NFS server, for example. In this scenario, you would like to read archives from NFS but expand their contents somewhere else.

In other words, create an additional {{ solr_downloads }} which is intended to keep the download binary. If it is already there, like in the example of a read-only NFS server, nothing needs to be downloaded.

[geerlingguy]

Closing in favor of #58—with that, you should not need to preserve the downloaded Solr archive anymore.