test: Add includefile for arrays

test: Add includefile for arrays

Otherwise Clang will complain on FreeBSD:
```
/home/jenkins/workspace/ceph-master/src/test/test_weighted_shuffle.cc:9:23: error: implicit instantiation of undefined template 'std::__1::array<char, 5>'
  std::array<char, 5> choices{'a', 'b', 'c', 'd', 'e'};
                      ^
/usr/include/c++/v1/__tuple:223:64: note: template is declared here
template <class _Tp, size_t _Size> struct _LIBCPP_TEMPLATE_VIS array;
                                                               ^
/home/jenkins/workspace/ceph-master/src/test/test_weighted_shuffle.cc:10:22: error: implicit instantiation of undefined template 'std::__1::array<int, 5>'
  std::array<int, 5> weights{100, 50, 25, 10, 1};
                     ^
/usr/include/c++/v1/__tuple:223:64: note: template is declared here
template <class _Tp, size_t _Size> struct _LIBCPP_TEMPLATE_VIS array;
```

Signed-off-by: Willem Jan Withagen <wjw@digiware.nl>