Update local ssd support for n2 and n2d machine types

[jossy]

Newer machine types like n2 and n2d require a minimum number of local ssds to be requested depending on the number of vCPUs. In order to be able to create larger VMs with local ssds, this needs to be considered by the CPI.
We are using a patched version of the CPI at the moment to address this, but ideally we would like to get this merged.

More details here:
https://cloud.google.com/compute/docs/disks/local-ssd#lssd_disk_options

[jpalermo]

Validated that without this patch it breaks when using larger n2 instance types.

With the patch I validated that it works with both larger n2 instance types specified via machine_type in the cloud properties.

Also validated that it works when specifying n2 as the machine_series and then specifying cpu and ram properties to create a custom n2 VM.

This doesn't seem to affect custom VMs created by only specifying cpu and ram.

Currently the additional local disks are not mounted by the agent. So if somebody wanted to make use of them, they'd have to do the mounting themself. We could update the bosh agent to mount them in the future, although without a good use case, it's hard to speculate how best to do that.