Fix Start-FileDownload retry logic
Fix Start-FileDownload retry logic

The '--retry' parameter from curl works only when the initial
connection is not successfully established.

If the connection drops during a file download with curl, the
retry logic is not executed.

This commit drops the '--retry' parameter from curl, and adds
the Start-ExecuteWithRetry wrapper over the curl exec call.

ionutbalutoiu/mesos-jenkins,ionutbalutoiu/mesos-jenkins