tests: Add a few simple tests

Add a few tests for the sign, verify, attach and detach code. These
require some additional infrastructure to create a sample PE/COFF
executable, plus a key & cert for testing.

Signed-off-by: Jeremy Kerr <jeremy.kerr@canonical.com>

tests/sign-attach-verify.sh

@@ -0,0 +1,12 @@
+#!/bin/bash -e
+
+. "$srcdir/common.sh"
+
+sig=test.sig
+signed=test.signed
+
+trap 'rm -f "$sig" "$signed"' EXIT
+
+"$sbsign" --cert "$cert" --key "$key" --detached --output $sig "$image"
+"$sbattach" --attach $sig $signed
+"$sbverify" --cert "$cert" "$signed"