Will not reuse manifest if reuse_logs options is false.

Prior implementation would always try to reuse the manifest, even if reuse_logs
was false (the default). This was missed because the stock
Env::NewAppendableFile implementation returns false forcing the creation of a
new log.

db/version_set.cc

@@ -1017,6 +1017,9 @@ Status VersionSet::Recover(bool *save_manifest) {
 
 bool VersionSet::ReuseManifest(const std::string& dscname,
                                const std::string& dscbase) {
+  if (!options_->reuse_logs) {
+    return false;
+  }
   FileType manifest_type;
   uint64_t manifest_number;
   uint64_t manifest_size;