Avoids panics when VM type isn't found during scale from zero (#78)

- Cluster autoscaler was trying to fetch VM details for AWS VMs instead of required Azure VMs for MCM (OOT) provider Azure. This lead to panics. Now, it fetches the details from the correct provider VM map.
- This PR also improves error handling in such scenarios to not panic.

cluster-autoscaler/cloudprovider/mcm/mcm_manager.go

@@ -628,7 +628,10 @@ func (m *McmManager) GetMachineDeploymentNodeTemplate(machinedeployment *Machine
 		if err != nil {
 			return nil, fmt.Errorf("Unable to fetch AWSMachineClass object %s, Error: %v", machineClass.Name, err)
 		}
-		awsInstance := aws.InstanceTypes[mc.Spec.MachineType]
+		awsInstance, exists := aws.InstanceTypes[mc.Spec.MachineType]
+		if !exists {
+			return nil, fmt.Errorf("Unable to fetch details for VM type %s", mc.Spec.MachineType)
+		}
 		instance = instanceType{
 			InstanceType: awsInstance.InstanceType,
 			VCPU:         awsInstance.VCPU,
@@ -642,7 +645,10 @@ func (m *McmManager) GetMachineDeploymentNodeTemplate(machinedeployment *Machine
 		if err != nil {
 			return nil, fmt.Errorf("Unable to fetch AzureMachineClass object %s, Error: %v", machineClass.Name, err)
 		}
-		azureInstance := azure.InstanceTypes[mc.Spec.Properties.HardwareProfile.VMSize]
+		azureInstance, exists := azure.InstanceTypes[mc.Spec.Properties.HardwareProfile.VMSize]
+		if !exists {
+			return nil, fmt.Errorf("Unable to fetch details for VM type %s", mc.Spec.Properties.HardwareProfile.VMSize)
+		}
 		instance = instanceType{
 			InstanceType: azureInstance.InstanceType,
 			VCPU:         azureInstance.VCPU,
@@ -666,7 +672,10 @@ func (m *McmManager) GetMachineDeploymentNodeTemplate(machinedeployment *Machine
 				return nil, fmt.Errorf("Unable to convert from %s to %s for %s, Error: %v", kindMachineClass, providerAWS, machinedeployment.Name, err)
 			}
 
-			awsInstance := aws.InstanceTypes[providerSpec.MachineType]
+			awsInstance, exists := aws.InstanceTypes[providerSpec.MachineType]
+			if !exists {
+				return nil, fmt.Errorf("Unable to fetch details for VM type %s", providerSpec.MachineType)
+			}
 			instance = instanceType{
 				InstanceType: awsInstance.InstanceType,
 				VCPU:         awsInstance.VCPU,
@@ -681,8 +690,10 @@ func (m *McmManager) GetMachineDeploymentNodeTemplate(machinedeployment *Machine
 			if err != nil {
 				return nil, fmt.Errorf("Unable to convert from %s to %s for %s, Error: %v", kindMachineClass, providerAzure, machinedeployment.Name, err)
 			}
-
-			azureInstance := aws.InstanceTypes[providerSpec.Properties.HardwareProfile.VMSize]
+			azureInstance, exists := azure.InstanceTypes[providerSpec.Properties.HardwareProfile.VMSize]
+			if !exists {
+				return nil, fmt.Errorf("Unable to fetch details for VM type %s", providerSpec.Properties.HardwareProfile.VMSize)
+			}
 			instance = instanceType{
 				InstanceType: azureInstance.InstanceType,
 				VCPU:         azureInstance.VCPU,