Fix coverity issues compaction_job, compaction_picker

Summary:
db/compaction_job.cc:
  ReportStartedCompaction(compaction);

CID 1419863 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
2. uninit_member: Non-static class member bottommost_level_ is not initialized in this constructor nor in any functions that it calls.

db/compaction_picker_universal.cc:
7struct InputFileInfo {
   	2. uninit_member: Non-static class member level is not initialized in this constructor nor in any functions that it calls.

CID 1405355 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
4. uninit_member: Non-static class member index is not initialized in this constructor nor in any functions that it calls.
 38  InputFileInfo() : f(nullptr) {}

db/dbformat.h:
 ParsedInternalKey()
 84      : sequence(kMaxSequenceNumber)  // Make code analyzer happy

CID 1168095 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
2. uninit_member: Non-static class member type is not initialized in this constructor nor in any functions that it calls.
 85  {}  // Intentionally left uninitialized (for speed)
Closes https://github.com/facebook/rocksdb/pull/3091

Differential Revision: D6534558

Pulled By: yiwu-arbug

fbshipit-source-id: 5ada975956196d267b3f149386842af71eda7553

db/compaction_job.cc

@@ -297,6 +297,7 @@ CompactionJob::CompactionJob(
       snapshot_checker_(snapshot_checker),
       table_cache_(std::move(table_cache)),
       event_logger_(event_logger),
+      bottommost_level_(false),
       paranoid_file_checks_(paranoid_file_checks),
       measure_io_stats_(measure_io_stats),
       write_hint_(Env::WLTH_NOT_SET) {

db/compaction_picker_universal.cc

@@ -35,7 +35,7 @@ namespace {
 // and the index of the file in that level
 
 struct InputFileInfo {
-  InputFileInfo() : f(nullptr) {}
+  InputFileInfo() : f(nullptr), level(0), index(0) {}
 
   FileMetaData* f;
   size_t level;