Rename a group of tests

Signed-off-by: John Else <john.else@citrix.com>
Improve unit tests for passthrough VGPUs

When creating a passthrough VGPU on a PGPU, create a VM and mark it as
attached to the PGPU's PCI device.

Signed-off-by: John Else <john.else@citrix.com>
CP-5923: More unit tests

Signed-off-by: John Else <john.else@citrix.com>
CP-5923: Add passthrough VGPU types to PGPU capacity checks

Signed-off-by: John Else <john.else@citrix.com>
Simplify the pgpu_helpers unit tests

Signed-off-by: John Else <john.else@citrix.com>
CP-5923: Add more tests of the PGPU capacity checks

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #1459 from johnelse/pgpu-helpers-more-tests

More unit tests for Xapi_pgpu_helpers.ml