run-tests.sh: Update Ubuntu Rpi image to 20.04

Changelog: None

Signed-off-by: Lluis Campos <lluis.campos@northern.tech>

scripts/test/run-tests.sh

@@ -29,7 +29,7 @@ RASPBIAN_IMAGE_URL="http://downloads.raspberrypi.org/raspbian_lite/images/raspbi
 UBUNTU_IMAGE_URL="https://downloads.mender.io/mender-convert/images/Ubuntu-Bionic-x86-64.img.gz"
 
 ## Auto-update
-UBUNTU_SERVER_RPI_IMAGE_URL="http://cdimage.ubuntu.com/ubuntu/releases/18.04.5/release/ubuntu-18.04.5-preinstalled-server-armhf+raspi3.img.xz"
+UBUNTU_SERVER_RPI_IMAGE_URL="http://cdimage.ubuntu.com/ubuntu/releases/20.04.2/release/ubuntu-20.04.2-preinstalled-server-armhf+raspi.img.xz"
 
 # Keep common function declarations in separate utils script
 UTILS_PATH=${0/$(basename $0)/test-utils.sh}