[NC-2105] Updated --bootnodes CLI option to take zero arguments, to configure Pantheon to run in 'bootnode' mode. (#548)

Signed-off-by: Adrian Sutton <adrian.sutton@consensys.net>

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

@@ -179,7 +179,7 @@ public class PantheonCommand implements DefaultCommandValues, Runnable {
         "Comma separated enode URLs for P2P discovery bootstrap. "
             + "Default is a predefined list.",
     split = ",",
-    arity = "1..*",
+    arity = "0..*",
     converter = EnodeToURIPropertyConverter.class
   )
   private final Collection<URI> bootstrapNodes = null;

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

@@ -489,6 +489,7 @@ public class PantheonCommandTest extends CommandTestAbstract {
     assertThat(commandErrorOutput.toString()).isEmpty();
   }
 
+  @Ignore("NC-2015 - Temporarily enabling zero-arg --bootnodes to permit 'bootnode' configuration")
   @Test
   public void callingWithBootnodesOptionButNoValueMustDisplayErrorAndUsage() {
     parseCommand("--bootnodes");
@@ -498,6 +499,21 @@ public class PantheonCommandTest extends CommandTestAbstract {
     assertThat(commandErrorOutput.toString()).startsWith(expectedErrorOutputStart);
   }
 
+  @Test
+  public void callingWithBootnodesOptionButNoValueMustPassEmptyBootnodeList() {
+    parseCommand("--bootnodes");
+
+    verify(mockRunnerBuilder).bootstrapPeers(uriListArgumentCaptor.capture());
+    verify(mockRunnerBuilder).build();
+
+    assertThat(uriListArgumentCaptor.getValue()).isEmpty();
+
+    assertThat(commandOutput.toString()).isEmpty();
+    assertThat(commandErrorOutput.toString()).isEmpty();
+  }
+
+  @Ignore(
+      "NC-2015 - Temporarily enabling zero-arg --bootnodes to permit 'bootnode' configuration, which changes the error.")
   @Test
   public void callingWithInvalidBootnodesMustDisplayErrorAndUsage() {
     parseCommand("--bootnodes", "invalid_enode_url");
@@ -507,6 +523,14 @@ public class PantheonCommandTest extends CommandTestAbstract {
     assertThat(commandErrorOutput.toString()).startsWith(expectedErrorOutputStart);
   }
 
+  @Test
+  public void callingWithInvalidBootnodesAndZeroArityMustDisplayAlternateErrorAndUsage() {
+    parseCommand("--bootnodes", "invalid_enode_url");
+    assertThat(commandOutput.toString()).isEmpty();
+    final String expectedErrorOutputStart = "Unmatched argument: invalid_enode_url";
+    assertThat(commandErrorOutput.toString()).startsWith(expectedErrorOutputStart);
+  }
+
   @Test
   public void callingWithBannedNodeidsOptionButNoValueMustDisplayErrorAndUsage() {
     parseCommand("--banned-nodeids");