honor task user when execing into raw_exec task (#9439)

Fix #9210 .

This update the executor so it honors the User when using nomad alloc exec. The bug was that the exec task didn't honor the init command when execing.

drivers/shared/executor/executor_basic.go

@@ -3,6 +3,8 @@
 package executor
 
 import (
+	"os/exec"
+
 	hclog "github.com/hashicorp/go-hclog"
 	"github.com/hashicorp/nomad/plugins/drivers"
 )
@@ -15,8 +17,6 @@ func NewExecutorWithIsolation(logger hclog.Logger) Executor {
 
 func (e *UniversalExecutor) configureResourceContainer(_ int) error { return nil }
 
-func (e *UniversalExecutor) runAs(_ string) error { return nil }
-
 func (e *UniversalExecutor) getAllPids() (map[int]*nomadPid, error) {
 	return getAllPidsByScanning()
 }
@@ -28,3 +28,5 @@ func (e *UniversalExecutor) start(command *ExecCommand) error {
 func withNetworkIsolation(f func() error, _ *drivers.NetworkIsolationSpec) error {
 	return f()
 }
+
+func setCmdUser(*exec.Cmd, string) error { return nil }