test: add end-to-end testing framework (#5435)

Partial fix for #5291. For details, see [README.md](https://github.com/tendermint/tendermint/blob/erik/e2e-tests/test/e2e/README.md) and [RFC-001](https://github.com/tendermint/tendermint/blob/master/docs/rfc/rfc-001-end-to-end-testing.md).

This only includes a single test case under `test/e2e/tests/`, as a proof of concept - additional test cases will be submitted separately. A randomized testnet generator will also be submitted separately, there a currently just a handful of static testnets under `test/e2e/networks/`. This will eventually replace the current P2P tests and run in CI.

test/e2e/runner/exec.go

@@ -0,0 +1,50 @@
+//nolint: gosec
+package main
+
+import (
+	"fmt"
+	"os"
+	osexec "os/exec"
+	"path/filepath"
+)
+
+// execute executes a shell command.
+func exec(args ...string) error {
+	cmd := osexec.Command(args[0], args[1:]...)
+	out, err := cmd.CombinedOutput()
+	switch err := err.(type) {
+	case nil:
+		return nil
+	case *osexec.ExitError:
+		return fmt.Errorf("failed to run %q:\n%v", args, string(out))
+	default:
+		return err
+	}
+}
+
+// execVerbose executes a shell command while displaying its output.
+func execVerbose(args ...string) error {
+	cmd := osexec.Command(args[0], args[1:]...)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	return cmd.Run()
+}
+
+// execCompose runs a Docker Compose command for a testnet.
+func execCompose(dir string, args ...string) error {
+	return exec(append(
+		[]string{"docker-compose", "-f", filepath.Join(dir, "docker-compose.yml")},
+		args...)...)
+}
+
+// execComposeVerbose runs a Docker Compose command for a testnet and displays its output.
+func execComposeVerbose(dir string, args ...string) error {
+	return execVerbose(append(
+		[]string{"docker-compose", "-f", filepath.Join(dir, "docker-compose.yml")},
+		args...)...)
+}
+
+// execDocker runs a Docker command.
+func execDocker(args ...string) error {
+	return exec(append([]string{"docker"}, args...)...)
+}