clean url path from double slashes

This PR clean out double slashes in url path. ie. "http://mirrors.us.kernel.org/centos/6/os/x86_64//../../isos/x86_64/CentOS-6.4-x86_64-netinstall.iso"

if not cleaned cURL will fail to download.

The PR also removes some trailing white spaces

Cheers,
Lars