osbuilder: Create guest image for SELinux

Create a guest image to support SELinux for containers inside the guest
if `SELINUX=yes` is specified. This works only if the guest rootfs is
CentOS and the init service is systemd, not the agent init. To enable
labeling the guest image on the host, selinuxfs must be mounted on the
host. The kata-agent will be labeled as `container_runtime_exec_t` type.

Fixes: #4812

Signed-off-by: Manabu Sugimoto <Manabu.Sugimoto@sony.com>

tools/osbuilder/scripts/lib.sh

@@ -79,7 +79,23 @@ gpgcheck=1
 gpgkey=file://${CONFIG_DIR}/${GPG_KEY_FILE}
 EOF
 	fi
-
+	if [ "$SELINUX" == "yes" ]; then
+		cat > "${DNF_CONF}" << EOF
+[appstream]
+name=${OS_NAME}-${OS_VERSION} upstream
+releasever=${OS_VERSION}
+EOF
+		echo "metalink=$METALINK_APPSTREAM" >> "$DNF_CONF"
+		if [ -n "$GPG_KEY_URL" ]; then
+			if [ ! -f "${CONFIG_DIR}/${GPG_KEY_FILE}" ]; then
+				curl -L "${GPG_KEY_URL}" -o "${CONFIG_DIR}/${GPG_KEY_FILE}"
+			fi
+			cat >> "${DNF_CONF}" << EOF
+gpgcheck=1
+gpgkey=file://${CONFIG_DIR}/${GPG_KEY_FILE}
+EOF
+		fi
+	fi
 }
 
 build_rootfs()