gtest: dynamically generate tests based on test machine's GPU count (#467)

* gtest: dynamically generate tests based on test machine's GPU count

* Adjust test element size and bfloat16 threshold for up to 16 GPUs

test/test_AllReduce.cpp

@@ -46,7 +46,7 @@ namespace CorrectnessTests
                              // Number of elements
                              testing::Values(1024, 1048576),
                              // Number of devices
-                             testing::Values(2,3,4,5,6,7,8),
+                             testing::Range(2,(GTESTS_NUM_GPUS+1)),
                              // In-place or not
                              testing::Values(false, true),
                              testing::Values("RCCL_ENABLE_CLIQUE=0", "RCCL_ENABLE_CLIQUE=1")),
@@ -71,7 +71,7 @@ namespace CorrectnessTests
                              // Number of elements
                              testing::Values(1024, 1048576),
                              // Number of devices
-                             testing::Values(2,3,4,5,6,7,8),
+                             testing::Range(2,(GTESTS_NUM_GPUS+1)),
                              // In-place or not
                              testing::Values(false, true),
                              testing::Values("RCCL_ENABLE_CLIQUE=0", "RCCL_ENABLE_CLIQUE=1")),