SOLR-6867: SolrCLI should check for existence before creating a new core/collection, more user-friendly error reporting (no stack trace), and the ability to pass a directory when using bin/solr to create a core or collection

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1647726 13f79535-47bb-0310-9956-ffa450edef68