Reformat imports to a consistent style for imports

rustfmt.toml configuration:
  imports_granularity = "One"
  group_imports = "One"

runtime/benches/accounts_index.rs

@@ -2,15 +2,17 @@
 
 extern crate test;
 
-use rand::{thread_rng, Rng};
-use solana_runtime::{
-    accounts_db::AccountInfo,
-    accounts_index::{
-        AccountSecondaryIndexes, AccountsIndex, ACCOUNTS_INDEX_CONFIG_FOR_BENCHMARKS,
+use {
+    rand::{thread_rng, Rng},
+    solana_runtime::{
+        accounts_db::AccountInfo,
+        accounts_index::{
+            AccountSecondaryIndexes, AccountsIndex, ACCOUNTS_INDEX_CONFIG_FOR_BENCHMARKS,
+        },
     },
+    solana_sdk::pubkey::{self, Pubkey},
+    test::Bencher,
 };
-use solana_sdk::pubkey::{self, Pubkey};
-use test::Bencher;
 
 #[bench]
 fn bench_accounts_index(bencher: &mut Bencher) {