e2e: add context to 'unable to init MCE device' error

Author: charludo

e2e/openssl/openssl_test.go

@@ -345,7 +345,9 @@ func TestOpenSSL(t *testing.T) {
 			"couldn't mount as ext2 due to feature incompatibilities",
 			// This started showing after upgrading the kernel from 6.12 to 6.16.
 			"tdx: VMM did not configure X2APIC_IDs properly",
-			// TODO(charludo): find out why this happens
+			// When both "quiet" and "systemd.show_status=false" are set in the commandline
+			// (e.g. default kata commandline), MCE can't enable its logger.
+			// See https://www.firstfloor.org/~andi/mce.pdf for details on MCE.
 			"mce: Unable to init MCE device (rc: -5)",
 		}
 		for line := range strings.SplitSeq(dmesgOutput, "\n") {