ds/random: fix threaded usage by switching to boost::random

The random threading unit test was failing on dss11-1gb oe-core
plarform with std random:

````
-------------------------------------------------------------------------------
dsRandomRandint each thread is randomly seeded
-------------------------------------------------------------------------------
../src/ds/random-test.cpp:54
...............................................................................

../src/ds/random-test.cpp:54: FAILED:
due to a fatal error condition:
  SIGINT - Terminal interrupt signal

````

Test passes on dss11-1gb oe-core plarform with boost random.

The used boost::random methods are header only,
no need to link boost::random

src/ds/random.cpp

@@ -24,12 +24,12 @@
 namespace ds {
 namespace detail {
 
-std::default_random_engine& getRandomEngine() {
+boost::random::minstd_rand& threadLocalRandomEngine() {
   // TODO(c++11): use thread_local std::unique_ptr
-  static boost::thread_specific_ptr<std::default_random_engine> engine;
+  static boost::thread_specific_ptr<boost::random::minstd_rand> engine;
   if (!engine.get()) {
     std::random_device device;
-    engine.reset(new std::default_random_engine(device()));
+    engine.reset(new boost::random::minstd_rand(device()));
   }
   return *engine;
 }

src/ds/random.h

@@ -18,20 +18,22 @@
 */
 #pragma once
 
-#include <random>
+#include <boost/random.hpp>
 
 namespace ds {
 
 namespace detail {
 /// Get thread local random engine initially seeded to random value.
-std::default_random_engine& getRandomEngine();
+///
+/// BUG: `std::default_random_engine` was failing with threads on oe-core platform
+boost::random::minstd_rand& threadLocalRandomEngine();
 } // detail
 
 /// Generates a random integer in the closed interval [a, b].
 /// Poor man's std::experimental::randint
 template <class IntType>
 IntType randint(IntType a, IntType b) {
-  return std::uniform_int_distribution<IntType>(a, b)(detail::getRandomEngine());
+  return boost::uniform_int<IntType>(a, b)(detail::threadLocalRandomEngine());
 }
 
 } // namespace ds