Disable DBTest.RepeatedWritesToSameKey (#1420)

Summary:
The verification condition of the test DBTest.RepeatedWritesToSameKey doesn't hold anymore after 3ce3bb3d.
Disable the test for now before we find a way to replace it.

Test Plan: Run the test and make sure it is disabled.

db/db_test.cc

@@ -1252,7 +1252,9 @@ TEST_F(DBTest, MinLevelToCompress2) {
   MinLevelHelper(this, options);
 }
 
-TEST_F(DBTest, RepeatedWritesToSameKey) {
+// This test may fail because of a legit case that multiple L0 files
+// are trivial moved to L1.
+TEST_F(DBTest, DISABLED_RepeatedWritesToSameKey) {
   do {
     Options options = CurrentOptions();
     options.env = env_;