Add GPU instances to CI infrastructure

This patch adds a small number of instances that include the
following specifications:

- 6 (dedicated) threads
- 60GB memory
- 225GB PCIe NVMe storage
- NVIDIA K80 GPU

This should hopefully help in adding CI coverage for vGPU
support.

Change-Id: If5b8f9cd305e2fd51b8dab315e4804ce7c628dfd

nodepool/nl03.openstack.org.yaml

@@ -34,6 +34,12 @@ labels:
     min-ready: 0
   - name: fedora-28-vexxhost
     min-ready: 1
+  - name: centos-7-gpu
+    min-ready: 0
+  - name: ubuntu-xenial-gpu
+    min-ready: 0
+  - name: ubuntu-bionic-gpu
+    min-ready: 0
 
 providers:
   - name: inap-mtl01
@@ -196,6 +202,24 @@ providers:
             flavor-name: 'kata-standard-4'
             diskimage: ubuntu-xenial
             key-name: infra-root-keys-2018-06-15
+      - name: gpu
+        max-servers: 2
+        labels:
+          - name: centos-7-gpu
+            min-ram: 8000
+            flavor-name: 'v2-gpu-6'
+            diskimage: centos-7
+            key-name: infra-root-keys-2018-06-15
+          - name: ubuntu-xenial-gpu
+            min-ram: 8000
+            flavor-name: 'v2-gpu-6'
+            diskimage: ubuntu-xenial
+            key-name: infra-root-keys-2018-06-15
+          - name: ubuntu-bionic-gpu
+            min-ram: 8000
+            flavor-name: 'v2-gpu-6'
+            diskimage: ubuntu-bionic
+            key-name: infra-root-keys-2018-06-15
 
   - name: vexxhost-sjc1
     region-name: sjc1