Install OS package via faasd-pro script

These packages need to be sourced by other means when
installing into an airgap, and you can set SKIP_OS=1 to avoid
using the Internet.

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

hack/install-pro.sh

@@ -5,7 +5,46 @@ if [ "$EUID" -ne 0 ]; then
     exit
 fi
 
-echo "1. Downloading OCI image, and installing pre-requisites"
+has_yum() {
+  [ -n "$(command -v yum)" ]
+}
+
+has_apt_get() {
+  [ -n "$(command -v apt-get)" ]
+}
+
+has_pacman() {
+  [ -n "$(command -v pacman)" ]
+}
+
+install_required_packages() {
+  if $(has_apt_get); then
+    # Debian bullseye is missing iptables. Added to required packages
+    # to get it working in raspberry pi. No such known issues in
+    # other distros. Hence, adding only to this block.
+    # reference: https://github.com/openfaas/faasd/pull/237
+    apt-get update -y
+    apt-get install -y curl runc bridge-utils iptables
+  elif $(has_yum); then
+    yum check-update -y
+    yum install -y curl runc iptables-services
+  elif $(has_pacman); then
+    pacman -Syy
+    pacman -Sy curl runc bridge-utils
+  else
+    fatal "Could not find apt-get, yum, or pacman. Cannot install dependencies on this OS."
+    exit 1
+  fi
+}
+
+echo "1. Installing required OS packages, set SKIP_OS=1 to skip this step"
+echo ""
+
+if [ -z "$SKIP_OS" ]; then
+    install_required_packages
+fi
+
+echo "2. Downloading OCI image, and installing pre-requisites"
 echo ""
 if [ ! -x "$(command -v arkade)" ]; then
     curl -sLS https://get.arkade.dev | sh
@@ -22,21 +61,13 @@ cd ${tmpdir}
 ./install.sh ./
 
 echo ""
-echo "2. You now need to activate your license via GitHub"
+echo "3. You now need to activate your license via GitHub"
 echo ""
 echo "sudo -E faasd github login"
 echo "sudo -E faasd activate"
 echo ""
 echo ""
-echo "3. Then perform the final installation steps"
+echo "4. Then perform the final installation steps"
 echo ""
 echo "sudo -E sh -c \"cd ${tmpdir}/var/lib/faasd && faasd install\""
 echo ""
-echo "4. Additional OS packages are sometimes required, with one of the below:"
-echo ""
-echo "apt install -qy runc bridge-utils iptables"
-echo ""
-echo "yum install runc iptables-services"
-echo ""
-echo "pacman -Sy runc bridge-utils"
-