r/virtual_machine: Validate exact disk type when using linked_clone

[vancluever]

A VM that's cloned with linked_clone and different disk mode options
that what is set on the source template will end up with inconsistent
settings post-clone, causing a read-update failure that will leave the
VM in a state that is irrecoverable to Terraform - the only way to
rectify the situation is to delete the VM and start over with a new
state.

This adds extra validation to make sure that thin_provisioned and
eagerly_scrub are set to the same settings as the source template's
counterpart disk, along with validating that the disk is the exact same
size (something that wasn't done yet).

Fixes #275.

---

PS: There will be a larger-ish PR (mainly because of adjustments to tests) that will follow this one to add thin_provisioned and eagerly_scrub attributes to the vsphere_virtual_machine data source. This will help ensure that these can be fetched in the same way we have the data source fetching disk_sizes currently.

[tombuildsstuff]

LGTM - assuming the tests pass 👍

[vancluever]

Thanks @tombuildsstuff! No regressions in a number of existing clone tests

=== RUN   TestAccResourceVSphereVirtualMachine
=== RUN   TestAccResourceVSphereVirtualMachine/clone_from_template
=== RUN   TestAccResourceVSphereVirtualMachine/clone,_multi-nic_(template_should_have_one)
=== RUN   TestAccResourceVSphereVirtualMachine/clone_with_different_timezone
=== RUN   TestAccResourceVSphereVirtualMachine/clone_with_bad_timezone
=== RUN   TestAccResourceVSphereVirtualMachine/clone_with_different_hostname
=== RUN   TestAccResourceVSphereVirtualMachine/clone_with_extra_disks
=== RUN   TestAccResourceVSphereVirtualMachine/clone_with_cdrom
--- PASS: TestAccResourceVSphereVirtualMachine (908.33s)
    --- PASS: TestAccResourceVSphereVirtualMachine/clone_from_template (124.53s)
    --- PASS: TestAccResourceVSphereVirtualMachine/clone,_multi-nic_(template_should_have_one) (122.93s)
    --- PASS: TestAccResourceVSphereVirtualMachine/clone_with_different_timezone (120.07s)
    --- PASS: TestAccResourceVSphereVirtualMachine/clone_with_bad_timezone (0.01s)
    --- PASS: TestAccResourceVSphereVirtualMachine/clone_with_different_hostname (120.03s)
    --- PASS: TestAccResourceVSphereVirtualMachine/clone_with_extra_disks (294.76s)
    --- PASS: TestAccResourceVSphereVirtualMachine/clone_with_cdrom (126.01s)