git clone https://git.launchpad.net/ubuntu/+source/goget-ubuntu-touch
build with crossbuilder

List of images ( channel is the path in system-image see https://system-image.ubports.com) :
goget-ubuntu-touch/obj-x86_64-linux-gnu/bin$ ./ubuntu-device-flash query --server=https://system-image.ubports.com --device=krillin --channel=ubports-touch/16.04/stable  --list-images

Install:
goget-ubuntu-touch/obj-x86_64-linux-gnu/bin$ ./ubuntu-device-flash touch --server=https://system-image.ubports.com --device=krillin --revision 23 --channel=ubports-touch/16.04/stable