Move detach flags to platform specific

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

snapshot/testsuite/helpers_linux.go

@@ -0,0 +1,5 @@
+package testsuite
+
+import "golang.org/x/sys/unix"
+
+const umountflags int = unix.MNT_DETACH

snapshot/testsuite/helpers_other.go

@@ -0,0 +1,5 @@
+// +build !linux
+
+package testsuite
+
+const umountflags int = 0

snapshot/testsuite/testsuite_unix.go

@@ -2,13 +2,7 @@
 
 package testsuite
 
-import (
-	"syscall"
-
-	"golang.org/x/sys/unix"
-)
-
-const umountflags int = unix.MNT_DETACH
+import "syscall"
 
 func clearMask() func() {
 	oldumask := syscall.Umask(0)

snapshot/testsuite/testsuite_windows.go

@@ -1,7 +1,5 @@
 package testsuite
 
-const umountflags int = 0
-
 func clearMask() func() {
 	return func() {}
 }