Temporarily disable hash index in stress tests (facebook#5792)

Summary:
PR facebook#4020 implicitly enabled the hash index as well in stress/crash
tests, resulting in assertion failures in Block. This patch disables
the hash index until we can pinpoint the root cause of these issues.
Pull Request resolved: facebook#5792

Test Plan:
Ran tools/db_crashtest.py and made sure it only uses index types 0 and 2
(binary search and partitioned index).

Differential Revision: D17346777

Pulled By: ltamasi

fbshipit-source-id: b4318f37f1fda3ee1bbff4ef2c2f556ca9e6b551

Author: ltamasi

tools/db_crashtest.py

@@ -41,7 +41,8 @@
     "enable_pipelined_write": 0,
     "expected_values_path": expected_values_file.name,
     "flush_one_in": 1000000,
-    "index_type": lambda: random.randint(0, 2),
+    # Temporarily disable hash index
+    "index_type": lambda: random.choice([0, 2]),
     "max_background_compactions": 20,
     "max_bytes_for_level_base": 10485760,
     "max_key": 100000000,