Fixed missing resource pool in linked clone from a template

At the moment `linked_clone` option works only from cloning from a virtual machine. Cloning from a template fails with the error:
```
InvalidArgument: A specified parameter was not correct.
spec.location.pool
No error message
```

This pull request fixes this issue by populating CloneSpec with resource pool value in both linked and not linked cloning cases.
Probably the same logic should be applied to datastore value, but I have no such environment to test, so leave this untouched.