Fix includes for env_test

Summary:
Previously compilation failed when ROCKSDB_NO_FBCODE=1 because fcntl.h
wasn't included for open().

Related issue: https://github.com/facebook/rocksdb/issues/977

Test Plan:
verified below command works now:

  $ make clean && ROCKSDB_NO_FBCODE=1 ROCKSDB_DISABLE_FALLOCATE=1 make -j32 env_test

Reviewers: sdong, yhchiang, igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D54135

util/env_test.cc

@@ -18,6 +18,7 @@
 #include <list>
 
 #ifdef OS_LINUX
+#include <fcntl.h>
 #include <linux/fs.h>
 #include <stdlib.h>
 #include <sys/stat.h>
@@ -26,7 +27,6 @@
 
 #ifdef ROCKSDB_FALLOCATE_PRESENT
 #include <errno.h>
-#include <fcntl.h>
 #endif
 
 #include "rocksdb/env.h"