os, syscall: skip tests when environment doesn't permit testing

Fixes #14693

Change-Id: Id0a6a80b4c37c0b0f1c2755667b7233ed8964e40
Reviewed-on: https://go-review.googlesource.com/20342
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/syscall/exec_linux_test.go b/src/syscall/exec_linux_test.go
index 6d31941..eb32cfd 100644
--- a/src/syscall/exec_linux_test.go
+++ b/src/syscall/exec_linux_test.go
@@ -31,6 +31,9 @@
 		if os.IsNotExist(err) {
 			t.Skip("kernel doesn't support user namespaces")
 		}
+		if os.IsPermission(err) {
+			t.Skip("unable to test user namespaces due to permissions")
+		}
 		t.Fatalf("Failed to stat /proc/self/ns/user: %v", err)
 	}
 	if isChrooted(t) {