Upload and download Fuel ISOs in scope of fuel-merge jobs

Upload and download Fuel ISOs in scope of fuel-merge jobs

This is the first step towards enabling virtual deployments for Fuel
merge jobs. This change introduces
- storing the ISOs built by the merge jobs on OPNFV Artifact Repository
- downloading ISOs built by the merge jobs for virtual deployments

Once this gets merged, a second change will be sent for enabling the virtual
deployments using downloaded ISO.

Change-Id: I726f58d914c7c216e1ffe626c2ca250f56d08222
Signed-off-by: Fatih Degirmenci <fatih.degirmenci@ericsson.com>