Fix sftp folder creation on promote-images.sh
Fix sftp folder creation on promote-images.sh

Fixes bug where sftp command does not have a "-p" parameter which
means that creating the file path need to ignore failure to create
a directory that already exists.

Adds validation of final URL at the end to avoid silent failures.

Change-Id: I8c4e23e99a6cc7d84e685c0d7354948072593112

rdo-infra/ci-config,rdo-infra/ci-config,rdo-infra/ci-config,redhat-openstack/rdo-infra,redhat-openstack/rdo-infra,rdo-infra/ci-config,redhat-openstack/rdo-infra,redhat-openstack/rdo-infra