x/sys/windows/svc/mgr: allow other ServiceType values in CreateService

Preserves SERVICE_WIN32_OWN_PROCESS as the default.

Fixes golang/go#14019

Change-Id: I764016c1b5ec5e1fe88ed39b9803754af966b2f3
Reviewed-on: https://go-review.googlesource.com/18760Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>

windows/svc/mgr/mgr.go

@@ -85,12 +85,15 @@ func (m *Mgr) CreateService(name, exepath string, c Config, args ...string) (*Se
 	if c.ErrorControl == 0 {
 		c.ErrorControl = ErrorNormal
 	}
+	if c.ServiceType == 0 {
+		c.ServiceType = windows.SERVICE_WIN32_OWN_PROCESS
+	}
 	s := syscall.EscapeArg(exepath)
 	for _, v := range args {
 		s += " " + syscall.EscapeArg(v)
 	}
 	h, err := windows.CreateService(m.Handle, toPtr(name), toPtr(c.DisplayName),
-		windows.SERVICE_ALL_ACCESS, windows.SERVICE_WIN32_OWN_PROCESS,
+		windows.SERVICE_ALL_ACCESS, c.ServiceType,
 		c.StartType, c.ErrorControl, toPtr(s), toPtr(c.LoadOrderGroup),
 		nil, toStringBlock(c.Dependencies), toPtr(c.ServiceStartName), toPtr(c.Password))
 	if err != nil {