vmdk/*: Fix gosec Errors unhandled issues
vmdk/*: Fix gosec Errors unhandled issues

See,
$ gometalinter --vendor --disable-all --enable=gosec --deadline 10m ./vmdk/...
vmdk/import.go:73::warning: Errors unhandled.,LOW,HIGH (gosec)
vmdk/import.go:75::warning: Errors unhandled.,LOW,HIGH (gosec)
vmdk/import.go:296::warning: Errors unhandled.,LOW,HIGH (gosec)

vmware/govmomi,bruceadowns/govmomi,vmware/govmomi,bruceadowns/govmomi,vmware/govmomi,bruceadowns/govmomi