Improve usability and better output formatting for gosndc

Description

Related Issue

#188 (closed)

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

cli/adapter/PndAdapter.go

@@ -197,24 +197,22 @@ func (p *PndAdapter) Endpoint() string {
 
 // PendingChanges sends an API call to the controller requesting
 // the UUIDs of all pending changes
-func (p *PndAdapter) PendingChanges() []uuid.UUID {
+func (p *PndAdapter) PendingChanges() ([]uuid.UUID, error) {
 	resp, err := api.GetChanges(p.endpoint, p.id.String())
 	if err != nil {
-		log.Error(err)
-		return nil
+		return nil, err
 	}
-	return filterChanges(ppb.ChangeState_CHANGE_STATE_PENDING, resp)
+	return filterChanges(ppb.ChangeState_CHANGE_STATE_PENDING, resp), nil
 }
 
 // CommittedChanges sends an API call to the controller requesting
 // the UUIDs of all committed changes
-func (p *PndAdapter) CommittedChanges() []uuid.UUID {
+func (p *PndAdapter) CommittedChanges() ([]uuid.UUID, error) {
 	resp, err := api.GetChanges(p.endpoint, p.id.String())
 	if err != nil {
-		log.Error(err)
-		return nil
+		return nil, err
 	}
-	return filterChanges(ppb.ChangeState_CHANGE_STATE_COMMITTED, resp)
+	return filterChanges(ppb.ChangeState_CHANGE_STATE_COMMITTED, resp), nil
 }
 
 // GetChange sends an API call to the controller requesting the specified change