Join pci_devices for servers API

A previous change, 119e2a690a64fdfd541010590285f754b3393653, joined
pci_devices in the v3 servers API when getting a full list of instances.
This was to work around a race condition with the PCI API extension.
When the PCI extension runs later, it lazy-loads pci_devices.  This may
raise InstanceNotFound if the instance was deleted in the meantime.

The last patch did not fully resolve this race condition, as we are also
seeing it rather regularly in API calls for a single server.  This patch
updates the compute_api.get() calls to join pci_devices, as well.

Change-Id: Id3e60c3c56c2eb4209e8aca8a2c26881ca86b435
Closes-bug: #1270680