cli/cmd: make clusterExists return error

To remove a dependency on log.Entry to make moving this code around
easier and to avoid hiding function complexity from logger.

Also, it no longer requires logger, so argument has been removed.

Part of #630

Signed-off-by: Mateusz Gozdek <mateusz@kinvolk.io>

cli/cmd/cluster-apply.go

@@ -69,7 +69,11 @@ func clusterApply(contextLogger *log.Entry) error {
 		return fmt.Errorf("initializing: %w", err)
 	}
 
-	exists := clusterExists(contextLogger, &c.terraformExecutor)
+	exists, err := clusterExists(c.terraformExecutor)
+	if err != nil {
+		return fmt.Errorf("checking if cluster exists: %w", err)
+	}
+
 	if exists && !confirm {
 		// TODO: We could plan to a file and use it when installing.
 		if err := c.terraformExecutor.Plan(); err != nil {

cli/cmd/cluster-destroy.go

@@ -53,7 +53,12 @@ func clusterDestroy(contextLogger *log.Entry) error {
 		return fmt.Errorf("initializing: %w", err)
 	}
 
-	if !clusterExists(contextLogger, &c.terraformExecutor) {
+	exists, err := clusterExists(c.terraformExecutor)
+	if err != nil {
+		return fmt.Errorf("checking if cluster exists: %w", err)
+	}
+
+	if !exists {
 		contextLogger.Println("Cluster already destroyed, nothing to do")
 
 		return nil

cli/cmd/cluster.go

@@ -148,14 +148,14 @@ func initializeTerraform(p platform.Platform, b backend.Backend) (*terraform.Exe
 // clusterExists determines if cluster has already been created by getting all
 // outputs from the Terraform. If there is any output defined, it means 'terraform apply'
 // run at least once.
-func clusterExists(contextLogger *log.Entry, ex *terraform.Executor) bool {
+func clusterExists(ex terraform.Executor) (bool, error) {
 	o := map[string]interface{}{}
 
 	if err := ex.Output("", &o); err != nil {
-		contextLogger.Fatalf("Failed to check if cluster exists: %v", err)
+		return false, fmt.Errorf("getting Terraform output: %w", err)
 	}
 
-	return len(o) != 0
+	return len(o) != 0, nil
 }
 
 type controlplaneUpdater struct {