NIFI-8300 Make non-source processors invalid if scheduled for Primary…

… Node only

This closes apache#4913.

Signed-off-by: Mark Payne <markap14@hotmail.com>

nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-framework-components/src/main/java/org/apache/nifi/controller/StandardProcessorNode.java

@@ -1090,6 +1090,13 @@ protected Collection<ValidationResult> computeValidationErrors(final ValidationC
                     break;
                 }
             }
+
+            // Ensure that execution node will not be misused
+            if (getExecutionNode() == ExecutionNode.PRIMARY && hasIncomingConnection()) {
+                results.add(new ValidationResult.Builder()
+                        .explanation("Processors with incoming connections cannot be scheduled for Primary Node Only.")
+                        .subject("Execution Node").valid(false).build());
+            }
         } catch (final Throwable t) {
             LOG.error("Failed to perform validation", t);
             results.add(new ValidationResult.Builder().explanation("Failed to run validation due to " + t.toString())