doc: Stop skopeo being installed by default

With the new rust image pull service skopeo we can parameterise whether to build
and install skopeo and turn it off by default if we don't need
signature verification support

Fixes: #3170

Signed-off-by: stevenhorsman <steven@uk.ibm.com>

docs/how-to/ccv0.sh

@@ -232,7 +232,7 @@ create_a_local_rootfs() {
     cd ${katacontainers_repo_dir}/tools/osbuilder/rootfs-builder
     export distro="ubuntu"
     [[ -z "${USE_PODMAN:-}" ]] && use_docker="${use_docker:-1}"
-    sudo -E OS_VERSION="${OS_VERSION:-}" GOPATH=$GOPATH DEBUG="${DEBUG}" USE_DOCKER="${use_docker:-}" SKOPEO_UMOCI=yes SECCOMP=yes ./rootfs.sh -r ${ROOTFS_DIR} ${distro}
+    sudo -E OS_VERSION="${OS_VERSION:-}" GOPATH=$GOPATH DEBUG="${DEBUG}" USE_DOCKER="${use_docker:-}" SKOPEO=${SKOPEO:-} UMOCI=yes SECCOMP=yes ./rootfs.sh -r ${ROOTFS_DIR} ${distro}
 
     # During the ./rootfs.sh call the kata agent is built as root, so we need to update the permissions, so we can rebuild it
     sudo chown -R ${USER}:${USER} "${katacontainers_repo_dir}/src/agent/"

docs/how-to/how-to-build-and-test-ccv0.md

@@ -35,6 +35,9 @@ In order to build, and demo the CCv0 functionality, these are the steps I take:
       If you want to build and run these you can export the `katacontainers_repo`, `katacontainers_branch`, `tests_repo`
       and `tests_branch` variables e.g. `export katacontainers_repo=github.com/stevenhorsman/kata-containers && export katacontainers_branch=stevenh/agent-pull-image-endpoint && export tests_repo=github.com/stevenhorsman/tests && export tests_branch=stevenh/add-ccvo-changes-to-build`
       before running the script.
+    - By default `ccv0.sh` enables the agent to use the rust implementation to pull container images on the guest. If
+      you wish to instead build and include the `skopeo` package for this then set `export SKOPEO=yes`. `skopeo` is
+      required for verifying container image signatures of pulled images.
 - Run the full build process with `. ~/ccv0.sh -d build_and_install_all`
     - *I run this script sourced just so that the required installed components are accessible on the `PATH` to the rest*
       *of the process without having to reload the session.*