remoteFileHandler: Add create exclusive option for truncateFile

Change-Id: Idfeff348e0f6fc240954e7d304b794dd99ea098c
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=979193
Signed-off-by: Yeela Kaplan <ykaplan@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/19022
Reviewed-by: Dan Kenigsberg <danken@redhat.com>