fix: e2e/alloc_logs: fail test if error is nil (#26980)

The comment was correct:

	// Run the alloc logs command which we expect to capture both stdout and
	// stderr logs. The command will reach its timeout and therefore return an
	// error. We want to ignore this, as it's expected. Any other error is
	// terminal.

but the test was actually passing if the command was not returning an error.

Author: marco-m

e2e/alloc_logs/alloc_logs_test.go

@@ -41,8 +41,6 @@ func testMixedFollow(t *testing.T) {
 	// error. We want to ignore this, as it's expected. Any other error is
 	// terminal.
 	out, err := e2eutil.Command("nomad", "alloc", "logs", "-f", allocStubs[0].ID)
-	if err != nil {
-		must.ErrorContains(t, err, "failed: signal: killed")
-	}
+	must.ErrorContains(t, err, "failed: signal: killed")
 	must.StrContains(t, out, "stdout\nstderr")
 }

e2e/e2eutil/cli.go

@@ -20,7 +20,9 @@ import (
 )
 
 // Command sends a command line argument to Nomad and returns the unbuffered
-// stdout as a string (or, if there's an error, the stderr)
+// stdout as a string (or, if there's an error, the stderr).
+// If the timeout expires, exec.CommandContext will send a kill signal to the process,
+// so the error will contain the string "signal: killed".
 func Command(cmd string, args ...string) (string, error) {
 	ctx, cancel := context.WithTimeout(context.Background(), time.Second*10)
 	defer cancel()