SLING-3463 - Config files cannot be installed via FileProvider on Windows

Preprocessing the  path to use forward slash so that later logic works properly

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1579534 13f79535-47bb-0310-9956-ffa450edef68
SLING-3463 - Config files cannot be installed via FileProvider on Windows

Adding testcase

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1579536 13f79535-47bb-0310-9956-ffa450edef68