Fix SELinux failures on disabled SELinux Machines

On some machines when setting the SELinux key labels to "", we are seeing
failures that cause runc to fail.  Even if SELinux is disabled.

This check will ignore callers calling SELinux Set*Label functions with ""
when SELinux is disabled.

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

vendor/github.com/opencontainers/selinux/go-selinux/selinux_linux.go

@@ -333,6 +333,11 @@ func writeCon(fpath string, val string) error {
 	if fpath == "" {
 		return ErrEmptyPath
 	}
+	if val == "" {
+		if !GetEnabled() {
+			return nil
+		}
+	}
 
 	out, err := os.OpenFile(fpath, os.O_WRONLY, 0)
 	if err != nil {