Airskiff: update packages prior to delete

Previously, airskiff's 000-install-packages script added the docker
repo, then deleted stale docker packages, then updated the apt database.
This change moves the apt update before the delete, so that apt-get
knows about the packages it's being asked to delete.  Without this in
place it'll fail on a fresh VM that doesn't know about the docker repo.

Change-Id: If009d8371c3ff49e4ed50599d8d62072868a84bf

tools/deployment/airskiff/developer/000-install-packages.sh

@@ -23,13 +23,13 @@ sudo apt-add-repository \
         "deb [arch=amd64] https://download.docker.com/linux/ubuntu \
         $(lsb_release -cs) \
         stable"
+sudo apt-get update
 
 # Purge Docker and install Docker CE
 sudo systemctl unmask docker.service
 sudo apt-get remove --no-install-recommends -y docker docker-engine docker.io
 
 # TODO(drewwalters96): Update to Docker 18.09 when supported by Minikube.
-sudo apt-get update
 sudo apt-get install --allow-downgrades --no-install-recommends -y \
         apparmor \
         ca-certificates \