Fix crash test allocation error under TSAN

Summary:
We were seeing the following error: "ThreadSanitizer: DenseSlabAllocator overflow. Dying."

It is fixable by mmap'ing a smaller region for keys' expected values, which this PR achieves by reducing the number of keys.
Closes https://github.com/facebook/rocksdb/pull/3803

Differential Revision: D7874478

Pulled By: ajkr

fbshipit-source-id: 433939f5cb92410ab4777d540cb0cc2ee0fe6c2e

Makefile

@@ -224,6 +224,9 @@ ifdef COMPILE_WITH_TSAN
 	PROFILING_FLAGS =
 	# LUA is not supported under TSAN
 	LUA_PATH =
+	# Limit keys for crash test under TSAN to avoid error:
+	# "ThreadSanitizer: DenseSlabAllocator overflow. Dying."
+	CRASH_TEST_EXT_ARGS += --max_key=1000000
 endif
 
 # AIX doesn't work with -pg