Boot criterion (#1032)

* Revert benchmarks back to libtest

Criterion has too many dependencies, it's execution as slower, and
we didn't see the kind of precision we had hoped for to use it to
block CI builds.

* Ignore benchmarks that take more than a few milliseconds per iteration

* Revert "Ignore benchmarks that take more than a few milliseconds per iteration"

This reverts commit b87cdf6ef4.

* Don't run benchmarks in CI

They are already built in the nightly build. Executing them in CI
doesn't add much value until the results are precise enough to act
on.

benches/ledger.rs

@@ -1,15 +1,16 @@
-#[macro_use]
-extern crate criterion;
+#![feature(test)]
 extern crate solana;
+extern crate test;
 
-use criterion::{Bencher, Criterion};
 use solana::hash::{hash, Hash};
 use solana::ledger::{next_entries, reconstruct_entries_from_blobs, Block};
 use solana::packet::BlobRecycler;
 use solana::signature::{Keypair, KeypairUtil};
 use solana::transaction::Transaction;
 use std::collections::VecDeque;
+use test::Bencher;
 
+#[bench]
 fn bench_block_to_blobs_to_block(bencher: &mut Bencher) {
     let zero = Hash::default();
     let one = hash(&zero.as_ref());
@@ -25,16 +26,3 @@ fn bench_block_to_blobs_to_block(bencher: &mut Bencher) {
         assert_eq!(reconstruct_entries_from_blobs(blob_q).unwrap(), entries);
     });
 }
-
-fn bench(criterion: &mut Criterion) {
-    criterion.bench_function("bench_block_to_blobs_to_block", |bencher| {
-        bench_block_to_blobs_to_block(bencher);
-    });
-}
-
-criterion_group!(
-    name = benches;
-    config = Criterion::default().sample_size(2);
-    targets = bench
-);
-criterion_main!(benches);