Add support for loading keypairs from file

beacon_node/beacon_chain/test_harness/src/gen_keys.rs

@@ -0,0 +1,20 @@
+use clap::{value_t, ArgMatches};
+use log::debug;
+use std::path::Path;
+use types::test_utils::{generate_deterministic_keypairs, KeypairsFile};
+
+pub fn gen_keys(matches: &ArgMatches) {
+    let validator_count = value_t!(matches.value_of("validator_count"), usize)
+        .expect("Validator count is required argument");
+    let output_file = matches
+        .value_of("output_file")
+        .expect("Output file has a default value.");
+
+    let keypairs = generate_deterministic_keypairs(validator_count);
+
+    debug!("Writing keypairs to file...");
+
+    let keypairs_path = Path::new(output_file);
+
+    keypairs.to_raw_file(&keypairs_path, &keypairs).unwrap();
+}