This patch adds apt-transport-https to the list of things to install
before starting, as apt-transport-https isn't installed by default
in Debian. It also replaces the hardcoded "xenial" by
{{ ansible_distribution_release }}. Note that the later will also
help when switching from Xenial to Bionic.
Change-Id: I2e692c62162486be6506ba67cbb4d887262994b2
2e351cffb5