Updated hackfest_multivdu_vnf: changed image from US1604 to ubuntu20.04

Updated image used in VNF to Ubuntu 20.04.

added 3 commits

• aa32f7c1...4d42a6b9 - 2 commits from branch master
• b535efcc - Merge remote-tracking branch 'origin/master' into hackfest_multivdu

Compare with previous version

added 3 commits

• b535efcc...562b513c - 2 commits from branch master
• fb918b78 - Merge remote-tracking branch 'origin/master' into hackfest_multivdu

Compare with previous version

merged

mentioned in commit 5fe32766