Disable DBFlushTest.SyncFail and DBTest.GroupCommitTest on Travis (#4154)

Summary:
I am temporarily disabling DBFlushTest.SyncFail and DBTest.GroupCommitTest tests on Travis until we figure out the root-cause. These tests will still continue to run locally though.
I haven't been able to reproduce these failures locally so far (even on a [local Travis environment](https://docs.travis-ci.com/user/common-build-problems/#Troubleshooting-Locally-in-a-Docker-Image) ).

These tests  are failing way too frequently causing everyone to wonder why their PR failed on travis, and waste time in debugging.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4154

Differential Revision: D8907258

Pulled By: sagar0

fbshipit-source-id: f40068b16e9245fb3791b6a4796435d1ce1ed205

db/db_flush_test.cc

@@ -55,6 +55,9 @@ TEST_F(DBFlushTest, FlushWhileWritingManifest) {
 #endif  // ROCKSDB_LITE
 }
 
+#ifndef TRAVIS
+// Disable this test temporarily on Travis as it fails intermittently.
+// Github issue: #4151
 TEST_F(DBFlushTest, SyncFail) {
   std::unique_ptr<FaultInjectionTestEnv> fault_injection_env(
       new FaultInjectionTestEnv(env_));
@@ -92,6 +95,7 @@ TEST_F(DBFlushTest, SyncFail) {
   ASSERT_EQ(refs_before, cfd->current()->TEST_refs());
   Destroy(options);
 }
+#endif  // TRAVIS
 
 TEST_F(DBFlushTest, FlushInLowPriThreadPool) {
   // Verify setting an empty high-pri (flush) thread pool causes flushes to be

db/db_test.cc

@@ -2149,6 +2149,9 @@ static void GCThreadBody(void* arg) {
 
 }  // namespace
 
+#ifndef TRAVIS
+// Disable this test temporarily on Travis as it fails intermittently.
+// Github issue: #4151
 TEST_F(DBTest, GroupCommitTest) {
   do {
     Options options = CurrentOptions();
@@ -2195,6 +2198,7 @@ TEST_F(DBTest, GroupCommitTest) {
     ASSERT_GT(hist_data.average, 0.0);
   } while (ChangeOptions(kSkipNoSeekToLast));
 }
+#endif  // TRAVIS
 
 namespace {
 typedef std::map<std::string, std::string> KVMap;