Don't test process_vm_readv on Travis arches that use qemu

Author: geofft

test/sys/test_uio.rs

@@ -193,6 +193,9 @@ fn test_preadv() {
 
 #[test]
 #[cfg(any(target_os = "linux", target_os = "android"))]
+// qemu-user does not yet implement process_vm_readv, cf. PR #568
+#[cfg_attr(all(travis, any(target_arch = "arm", target_arch = "aarch64")),
+           ignore)]
 fn test_process_vm_readv() {
     use nix::unistd::ForkResult::*;
     use nix::sys::signal::*;