Prevent stalls in preshutdown tests

Summary:
The tests using sync_point for intent to shutdown stop
compaction and this results in stalls if too many rows are written. We
now limit the number of rows written to prevent stalls, since the focus
of the test is to cancel background work, which is being correctly
tested. This fixes a Jenkins issue.

Test Plan: DBTest.PreShutdown*

Reviewers: sdong, igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D34893

db/db_test.cc

@@ -10282,7 +10282,7 @@ TEST(DBTest, PreShutdownMultipleCompaction) {
   int max_operation_count[ThreadStatus::NUM_OP_TYPES] = {0};
   // check how many threads are doing compaction using GetThreadList
   int operation_count[ThreadStatus::NUM_OP_TYPES] = {0};
-  for (int file = 0; file < 64 * kNumL0Files; ++file) {
+  for (int file = 0; file < 8 * kNumL0Files; ++file) {
     for (int k = 0; k < kEntriesPerBuffer; ++k) {
       ASSERT_OK(Put(ToString(key++), RandomString(&rnd, kTestValueSize)));
     }
@@ -10368,7 +10368,7 @@ TEST(DBTest, PreShutdownCompactionMiddle) {
   int max_operation_count[ThreadStatus::NUM_OP_TYPES] = {0};
   // check how many threads are doing compaction using GetThreadList
   int operation_count[ThreadStatus::NUM_OP_TYPES] = {0};
-  for (int file = 0; file < 64 * kNumL0Files; ++file) {
+  for (int file = 0; file < 8 * kNumL0Files; ++file) {
     for (int k = 0; k < kEntriesPerBuffer; ++k) {
       ASSERT_OK(Put(ToString(key++), RandomString(&rnd, kTestValueSize)));
     }