SOLR-17104: Protect lib directories from being written to

[HoustonPutman]

https://issues.apache.org/jira/browse/SOLR-17104

[epugh]

Is this the only place where this is needed? Or are there lots of directories similar?

[HoustonPutman]

Do you mean the restore code or the lib directories?

For the restore code, there might be more places we are writing user provided files, but I can't think of it.

As for the lib directories, this is all of them off of my head, but I could be missing a few.

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