return error if context canceled during getting virtual machine images (#4415) (#4444)

if context deadline exceeded when retrieving vm metadata

we need correct error message instead of partially retrieving results
(cherry picked from commit e403941)

Author: hongtaiwang

tkg/vc/client.go

@@ -697,6 +697,9 @@ func (c *DefaultClient) GetVirtualMachineImages(ctx context.Context, datacenterM
 		if ovaVersion, distroName, distroVersion, distroArch := c.getVMMetadata(&vms[i]); ovaVersion != "" {
 			path, _, err := c.GetPath(ctx, vms[i].Self.Value)
 			if err != nil {
+				if ctx.Err() != nil {
+					return results, err
+				}
 				continue
 			}
 			obj := &tkgtypes.VSphereVirtualMachine{

tkg/vsphere-template-resolver/templateresolver/resolver_impl.go

@@ -38,6 +38,7 @@ func (r *Resolver) GetVSphereEndpoint(svrContext *VSphereContext) (vc.Client, er
 	vcURL.Path = "/sdk"
 
 	r.Log.Info(fmt.Sprintf("Creating client with endpoint: %v", vcURL))
+	// TODO: setup a cache to reuse vc sessions
 	vcClient, err := vc.NewClient(vcURL, svrContext.TLSThumbprint, svrContext.InsecureSkipVerify)
 	if err != nil {
 		return nil, errors.Wrap(err, "failed to create vc client")