Multiprocess unit test various fixes (#367)

* Re-enabling mp unit tests

* Fixing shared memory leak and other bugs related to shared mem for MP unit tests

* Revert 43bfbfc97bf9edbae1f386d461439091618ff8ed

* Further tightening up unlinks

* Moving test check macros to separate header file

* Tightening up shared memory unlinking for clique kernels, add munmap for host barrier for MP unit tests

* Updating new MP unit test

* Fixing mqueue bug

* Fixing memory leak in MP unit tests

[ROCm/rccl commit: 0b2bfdd6d8]

projects/rccl/test/test_AllReduceMultiProcess.cpp

@@ -31,6 +31,7 @@ namespace CorrectnessTests
     }
 
     ValidateProcesses(pids);
+    dataset->ReleaseRootProcess();
   }
 
   INSTANTIATE_TEST_SUITE_P(AllReduceMultiProcessCorrectnessSweep,