tools/db_crashtest2.py should run on the same DB

Summary:
Crash tests are supposed to restart the same DB after crashing, but it is now opening a different DB. Fix it.
It's probably a leftover of https://reviews.facebook.net/D17073

Test Plan: Run the test and make sure the same Db is opened.

Reviewers: kradhakrishnan, rven, igor, IslamAbdelRahman, yhchiang, anthony

Reviewed By: anthony

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D43197

tools/db_crashtest2.py

@@ -63,6 +63,7 @@ def main(argv):
     total_check_mode = 4
     check_mode = 0
 
+    dbname = tempfile.mkdtemp(prefix='rocksdb_crashtest_')
     while time.time() < exit_time:
         killoption = ""
         if check_mode == 0:
@@ -85,7 +86,6 @@ def main(argv):
             # normal run
             additional_opts = "--ops_per_thread=" + str(ops_per_thread)
 
-        dbname = tempfile.mkdtemp(prefix='rocksdb_crashtest_')
         cmd = re.sub('\s+', ' ', """
             ./db_stress
             --test_batches_snapshots=%s