fixed DBTest.GetPropertiesOfAllTablesTest and DBTest.GetUserDefinedTablaProperties flakiness

Summary: These tests used to fail if a compaction happened between flushing tables and enumerating them to get properties.

Test Plan: this reports occasional failures without this diff and no failures with it: `for i in {1..10000}; do echo $i; done | parallel --gnu -j100 'TEST_TMPDIR=`TMPDIR=/dev/shm/rockstemp mktemp -d -t` ./db_test --gtest_filter=DBTest.GetUserDefinedTablaProperties >&/dev/null || echo {} failed'`

Reviewers: sdong

Reviewed By: sdong

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D42861

db/db_test.cc

@@ -495,6 +495,7 @@ class CoutingUserTblPropCollectorFactory
 
 TEST_F(DBTest, GetUserDefinedTablaProperties) {
   Options options = CurrentOptions();
+  options.level0_file_num_compaction_trigger = (1<<30);
   options.max_background_flushes = 0;
   options.table_properties_collector_factories.resize(1);
   options.table_properties_collector_factories[0] =