yubihsm: show labels when listing keys (#102)

Makes it easier to determine which key is which

README.txsigner.md

@@ -202,8 +202,10 @@ Finally, confirm you see the key listed when you run
 ```
 $ tmkms yubihsm keys list
 Listing keys in YubiHSM #0001234567:
-- 0x0001: [cons] cosmosvalconspub1zcjduepqpxg30wtw7tlt750lhl3fdjfex6eq7tj3gfer3ugrzahd27srflhqv6ep6j
+- 0x0001: [cons] cosmosvalconspub...
+  [...]
 - 0x0123: [acct] terra13tdvxsauagu33glu74u93mdka7ahvm5a6yfr76
+   label: "columbus-3 oracle signer"
 ```
 
 If the newly generated account key is properly configured for the desired chain

src/commands/yubihsm/keys/list.rs

@@ -95,6 +95,17 @@ fn display_key_info(
     key: &yubihsm::object::Entry,
     key_formatters: &Map<u16, keyring::Format>,
 ) {
+    let key_info = hsm
+        .get_object_info(key.object_id, yubihsm::object::Type::AsymmetricKey)
+        .unwrap_or_else(|e| {
+            status_err!(
+                "couldn't get object info for asymmetric key #{}: {}",
+                key.object_id,
+                e
+            );
+            process::exit(1);
+        });
+
     let public_key = hsm.get_public_key(key.object_id).unwrap_or_else(|e| {
         status_err!(
             "couldn't get public key for asymmetric key #{}: {}",
@@ -142,4 +153,5 @@ fn display_key_info(
     };
 
     status_attr_ok!(key_id, "[{}] {}", key_type, key_serialized);
+    println!("   label: \"{}\"", &key_info.label);
 }