CloudSolrClient using unsplit collection list when expanding aliases

Some recent refactoring seems to have introduced a bug in SolrJ's CloudSolrClient, when it's expanding a collection list and resolving aliases, it's using the wrong local variable for the alias lookup. This leads to an exception because the value is not an alias.

E.g. suppose you made a request with &collection=x,y where either or both of x and y are not real collection names but valid aliases. This will fail, incorrectly, because the lookup is using x,y as a potential alias name lookup.

Patch to fix this attached, which was tested locally and fixed the issue.