unshare: fix creating a userns when running as root

this check would prevent the function to ever be used when running
as root, since we won't check what capabilities are currently
available to the process.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

pkg/unshare/unshare_linux.go

@@ -465,7 +465,7 @@ func bailOnError(err error, format string, a ...interface{}) { // nolint: golint
 // MaybeReexecUsingUserNamespace re-exec the process in a new namespace
 func MaybeReexecUsingUserNamespace(evenForRoot bool) {
 	// If we've already been through this once, no need to try again.
-	if os.Geteuid() == 0 && IsRootless() {
+	if os.Geteuid() == 0 && GetRootlessUID() > 0 {
 		return
 	}