Fix Cirrus/Packer VM image building

An invalid GCE value is being passed to packer, preventing it from
building VM images.  Fix this, and centralize the definition of the
image name suffix by setting it at ``setup_environment.sh`` call-time,
rather encoding inside packer's `libpod_images.json`.  This makes
the value available for use by other scripts.

Also, switch the unique component of the name, to be based on the
commit-sha being tested.  This will improve traceability, since the git
history is more permanent than the `CIRRUS_BUILD_ID` env. var.  The
later is subject to log-rotation, destroying evidence of the images
source state.

Signed-off-by: Chris Evich <cevich@redhat.com>

contrib/cirrus/setup_environment.sh

@@ -41,6 +41,7 @@ then
         "export OS_RELEASE_ID=\"$(os_release_id)\"" \
         "export OS_RELEASE_VER=\"$(os_release_ver)\"" \
         "export OS_REL_VER=\"${OS_RELEASE_ID}-${OS_RELEASE_VER}\"" \
+        "export BUILT_IMAGE_SUFFIX=\"-$CIRRUS_REPO_NAME-${CIRRUS_CHANGE_IN_REPO:0:8}\"" \
         "export GOPATH=\"/go\"" \
         'export PATH="$HOME/bin:$GOPATH/bin:/usr/local/bin:$PATH"' \
         'export LD_LIBRARY_PATH="/usr/local/lib${LD_LIBRARY_PATH:+:${LD_LIBRARY_PATH}}"'