clearfog: Install RAUC keyring

It seems that a certificate keychain is a required part here.

Change-Id: I25a6fa49c127154b2710ac92a0e2d284fae381cd
diff --git a/board/czechlight/common/install-rauc-cert.sh b/board/czechlight/common/install-rauc-cert.sh
new file mode 100755
index 0000000..bff359b
--- /dev/null
+++ b/board/czechlight/common/install-rauc-cert.sh
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+install -m 0644 -D ${BR2_EXTERNAL_CZECHLIGHT_PATH}/crypto/rauc-cert.pem $TARGET_DIR/etc/rauc/keyring.pem