[ubuntu] Refactor bash functions (#9055)

images/ubuntu/scripts/build/install-container-tools.sh

@@ -10,14 +10,14 @@ source $HELPER_SCRIPTS/os.sh
 # pin podman due to https://github.com/actions/runner-images/issues/7753
 #                   https://bugs.launchpad.net/ubuntu/+source/libpod/+bug/2024394
 #
-if isUbuntu20; then
+if is_ubuntu20; then
     install_packages=(podman buildah skopeo)
 else
     install_packages=(podman=3.4.4+ds1-1ubuntu1 buildah skopeo)
 fi
 
 # Packages is available in the official Ubuntu upstream starting from Ubuntu 21
-if isUbuntu20; then
+if is_ubuntu20; then
     REPO_URL="https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable"
     source /etc/os-release
     sh -c "echo 'deb ${REPO_URL}/x${NAME}_${VERSION_ID}/ /' > /etc/apt/sources.list.d/devel:kubic:libcontainers:stable.list"
@@ -31,7 +31,7 @@ apt-get -y install ${install_packages[@]}
 mkdir -p /etc/containers
 printf "[registries.search]\nregistries = ['docker.io', 'quay.io']\n" | tee /etc/containers/registries.conf
 
-if isUbuntu20; then
+if is_ubuntu20; then
     # Remove source repo
     rm /etc/apt/sources.list.d/devel:kubic:libcontainers:stable.list
     # Document source repo