Enhancement: should skip path check for tablets in trash (StarRocks#1180

)

If a tablet has been dropped but has not been removed from RocksDB, should skip
the garbage path checking for it.

perform_path_gc_by_tablet will do the following steps to decide whether a tablet directory can be removed:

Call TabletManager::get_tablet if see if the tablet is resident in memory and if so, skip deleting the directory
Read the RocksDB to see if the tablet meta exist in RocksDB and if so, skip deleting the directory
All above checks passed, begin to delete the directory.
For an already-dropped tablet but with its meta still existing in RocksDB, if we pass false as the second argument of TabletManager::get_tablet, the first two steps are required, but if we pass true as the argument, only the first step needed.

be/src/storage/data_dir.cpp

@@ -578,7 +578,7 @@ void DataDir::perform_path_gc_by_tablet() {
             LOG(WARNING) << "invalid tablet id " << tablet_id << " or schema hash " << schema_hash << ", path=" << path;
             continue;
         }
-        TabletSharedPtr tablet = _tablet_manager->get_tablet(tablet_id, false);
+        TabletSharedPtr tablet = _tablet_manager->get_tablet(tablet_id, true);
         if (tablet != nullptr) {
             // could find the tablet, then skip check it
             continue;