Fix: Skip sigul installation on Ubuntu

Skip sigul installation on Ubuntu, since the CentOS
docker container handles the installation during container
creation.

Issue: RELENG-5419
Change-Id: I716f4f36d90ddad648725ccbe9f8d48a74abd549
Signed-off-by: Anil Belur <abelur@linuxfoundation.org>

releasenotes/notes/skip-sigul-on-ubuntu--c8070cceaa577da1.yaml

@@ -0,0 +1,8 @@
+---
+issues:
+  - |
+    Sigul install is available only on CentOS based patforms.
+fixes:
+  - |
+    Skip sigul installation on Ubuntu, since the CentOS docker container handles
+    the installation during container creation.

shell/sigul-install.sh

@@ -13,6 +13,12 @@ echo "---> sigul-install.sh"
 # Ensure we fail the job if any steps fail.
 set -e -o pipefail
 
+OS=$(facter operatingsystem | tr '[:upper:]' '[:lower:]')
+if ! [[ "${OS}" =~ ^(fedora|centos|redhat) ]]; then
+    echo "INFO: Skip step, sigul install not available on platform ${OS}"
+    exit 0
+fi
+
 if command -v sigul &>/dev/null; then
     echo "Sigul already installed; skipping installation."
 else

shell/sigul-sign-dir.sh

@@ -19,8 +19,10 @@ set -e -o pipefail
 lf-activate-venv --python python3 lftools
 
 OS=$(facter operatingsystem | tr '[:upper:]' '[:lower:]')
-OS_RELEASE=$(facter lsbdistrelease | tr '[:upper:]' '[:lower:]')
-if [[ "$OS_RELEASE" == "8" && "$OS" == 'centos' ]]; then
+OS_DIST_RELEASE=$(facter lsbdistrelease | tr '[:upper:]' '[:lower:]')
+OS_RELEASE=$(facter operatingsystemrelease | tr '[:upper:]' '[:lower:]')
+if [[ "$OS_DIST_RELEASE" == "8" && "${OS}" =~ ^(fedora|centos|redhat)$ ]] || \
+   [[ "$OS_RELEASE" =~ ^(20.04|22.04)$ && "${OS}" =~ ^(ubuntu|debian)$ ]]; then
     # Get Dockerfile and the enterpoint to build the docker image.
     # shellcheck disable=SC2140
     wget -O "${WORKSPACE}/sigul-sign.sh" "https://raw.githubusercontent.com/"\