Add Env::SanitizeEnvOptions (#5885)

Summary:
Add Env::SanitizeEnvOptions to allow underlying environments properly
configure env options.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5885

Test Plan:
```
make check
```

Differential Revision: D17910327

Pulled By: riversand963

fbshipit-source-id: 86a1ac616e485742c35c4a9cc9f1227c529fc00f

env/env.cc

@@ -420,6 +420,7 @@ void AssignEnvOptions(EnvOptions* env_options, const DBOptions& options) {
       options.writable_file_max_buffer_size;
   env_options->allow_fallocate = options.allow_fallocate;
   env_options->strict_bytes_per_sync = options.strict_bytes_per_sync;
+  options.env->SanitizeEnvOptions(env_options);
 }
 
 }

include/rocksdb/env.h

@@ -528,6 +528,8 @@ class Env {
     return Status::NotSupported();
   }
 
+  virtual void SanitizeEnvOptions(EnvOptions* /*env_opts*/) const {}
+
   // If you're adding methods here, remember to add them to EnvWrapper too.
 
  protected:
@@ -1363,6 +1365,9 @@ class EnvWrapper : public Env {
   Status GetFreeSpace(const std::string& path, uint64_t* diskfree) override {
     return target_->GetFreeSpace(path, diskfree);
   }
+  void SanitizeEnvOptions(EnvOptions* env_opts) const override {
+    target_->SanitizeEnvOptions(env_opts);
+  }
 
  private:
   Env* target_;