treewide: add missing error handling

Change-Id: I55ccf3ff490b58f6af93e665c668428acddc8d65
Reviewed-on: https://review.monogon.dev/c/monogon/+/3019
Vouch-Run-CI: Tim Windelschmidt <tim@monogon.tech>
Tested-by: Jenkins CI
Reviewed-by: Serge Bazanski <serge@monogon.tech>
diff --git a/metropolis/installer/test/main.go b/metropolis/installer/test/main.go
index 3c2460a..b2fb8dc 100644
--- a/metropolis/installer/test/main.go
+++ b/metropolis/installer/test/main.go
@@ -273,6 +273,9 @@
 	}
 	// Verify that GPT exists.
 	ti, err := storage.GetPartitionTable()
+	if err != nil {
+		t.Fatalf("Couldn't read the installer image partition table: %s", err)
+	}
 	if ti.Type() != "gpt" {
 		t.Error("Couldn't verify that the resulting node image contains a GPT.")
 	}