hyperv: report disk_available_least field

Reporting the disk_available_least field can help in making sure
the scheduler doesn't pick a host that cannot fit a specific flavor's
disk.

The reported local_gb_used is calculated based on the instances spawned
by nova on a certain compute node, and might not reflect the actual
reality, especially on shared storage scenarios.

Change-Id: I20992acef119f11f6584094438043a760fc4a287
Closes-Bug: #1717892
(cherry picked from commit 6479f55)

compute_hyperv/nova/hostops.py

@@ -170,11 +170,17 @@ def get_available_resource(self):
                  cpu_topology['cores'] *
                  cpu_topology['threads'])
 
+        # NOTE(claudiub): free_hdd_gb only refers to the currently free
+        # physical storage, it doesn't take into consideration the virtual
+        # sizes of the VMs' dynamic disks. This means that the VMs' disks can
+        # expand beyond the free_hdd_gb's value, and instances will still be
+        # scheduled to this compute node.
         dic = {'vcpus': vcpus,
                'memory_mb': total_mem_mb,
                'memory_mb_used': used_mem_mb,
                'local_gb': total_hdd_gb,
                'local_gb_used': used_hdd_gb,
+               'disk_available_least': free_hdd_gb,
                'hypervisor_type': "hyperv",
                'hypervisor_version': self._get_hypervisor_version(),
                'hypervisor_hostname': self.get_hostname(),

compute_hyperv/tests/unit/test_hostops.py

@@ -203,6 +203,7 @@ def test_get_available_resource(self, mock_node,
                     'memory_mb_used': mock.sentinel.MEMORY_MB_USED,
                     'local_gb': mock.sentinel.LOCAL_GB,
                     'local_gb_used': mock.sentinel.LOCAL_GB_USED,
+                    'disk_available_least': mock.sentinel.LOCAL_GB_FREE,
                     'vcpus': self.FAKE_NUM_CPUS,
                     'vcpus_used': 0,
                     'hypervisor_type': 'hyperv',