Default node key location should always be under data dir

pantheon/src/main/java/tech/pegasys/pantheon/cli/PantheonCommand.java

@@ -150,9 +150,9 @@ public static class RpcApisConversionException extends Exception {
     names = {"--node-private-key"},
     paramLabel = MANDATORY_PATH_FORMAT_HELP,
     description =
-        "the path to the node's private key file. (default: a file named \"key\" in the Pantheon data folder.)"
+        "the path to the node's private key file (default: a file named \"key\" in the Pantheon data folder)"
   )
-  private final File nodePrivateKeyFile = KeyPairUtil.getDefaultKeyFile(dataDir);
+  private final File nodePrivateKeyFile = null;
 
   // Genesis file path with null default option if the option
   // is not defined on command line as this default is handled by Runner
@@ -452,14 +452,18 @@ PantheonController<?> buildController() {
           syncWithOttoman,
           new MiningParameters(coinbase, minTransactionGasPrice, extraData, isMiningEnabled),
           isDevMode,
-          nodePrivateKeyFile);
+          getNodePrivateKeyFile());
     } catch (final InvalidConfigurationException e) {
       throw new ExecutionException(new CommandLine(this), e.getMessage());
     } catch (final IOException e) {
       throw new ExecutionException(new CommandLine(this), "Invalid path", e);
     }
   }
 
+  private File getNodePrivateKeyFile() {
+    return nodePrivateKeyFile != null ? nodePrivateKeyFile : KeyPairUtil.getDefaultKeyFile(dataDir);
+  }
+
   private JsonRpcConfiguration jsonRpcConfiguration() {
     final JsonRpcConfiguration jsonRpcConfiguration = JsonRpcConfiguration.createDefault();
     jsonRpcConfiguration.setEnabled(isJsonRpcEnabled);

pantheon/src/test/java/tech/pegasys/pantheon/cli/PantheonCommandTest.java

@@ -369,7 +369,14 @@ public void dataDirOptionMustBeUsed() throws Exception {
     parseCommand("--datadir", path.toString());
 
     verify(mockControllerBuilder)
-        .build(any(), pathArgumentCaptor.capture(), any(), eq(false), any(), anyBoolean(), any());
+        .build(
+            any(),
+            pathArgumentCaptor.capture(),
+            any(),
+            eq(false),
+            any(),
+            anyBoolean(),
+            eq(path.resolve("key").toFile()));
 
     assertThat(pathArgumentCaptor.getValue()).isEqualByComparingTo(path);