utils: Improve containerd configuration

`kata-manager.sh` improvements for containerd:

- Fixed containerd default branch (which is now `main`).
- Only install service file if it doesn't already exist.
- Enable the containerd service to ensure it can be started.

Signed-off-by: James O. D. Hunt <james.o.hunt@intel.com>

utils/kata-manager.sh

@@ -391,12 +391,19 @@ configure_containerd()
 
 	local cfg="/etc/containerd/config.toml"
 
+	local systemd_unit_dir="/etc/systemd/system"
+	sudo mkdir -p "$systemd_unit_dir"
+
+	local dest="${systemd_unit_dir}/${containerd_service_name}"
+
+	if [ ! -f "$dest" ]
+	then
 		pushd "$tmpdir" >/dev/null
 
 		local service_url=$(printf "%s/%s/%s/%s" \
 			"https://raw.githubusercontent.com" \
 			"${containerd_slug}" \
-		"master" \
+			"main" \
 			"${containerd_service_name}")
 
 		curl -LO "$service_url"
@@ -405,10 +412,6 @@ configure_containerd()
 			"$(date -Iseconds)" |\
 			tee -a "$containerd_service_name"
 
-	local systemd_unit_dir="/etc/systemd/system"
-	sudo mkdir -p "$systemd_unit_dir"
-
-	local dest="${systemd_unit_dir}/${containerd_service_name}"
 
 		sudo cp "${containerd_service_name}" "${dest}"
 		sudo systemctl daemon-reload
@@ -416,6 +419,7 @@ configure_containerd()
 		info "Installed ${dest}"
 
 		popd >/dev/null
+	fi
 
 	# Backup the original containerd configuration:
 	sudo mkdir -p "$(dirname $cfg)"
@@ -448,6 +452,7 @@ EOT
 		info "Modified $cfg"
 	}
 
+	sudo systemctl enable containerd
 	sudo systemctl start containerd
 
 	info "Configured $project\n"