[vmhost] add available_ram_in_gb and available_cores

uncloud/uncloud_vm/models.py

@@ -45,6 +45,14 @@ class VMHost(models.Model):
     def vms(self):
         return VMProduct.objects.filter(vmhost=self)
 
+    @property
+    def available_ram_in_gb(self):
+        return self.usable_ram_in_gb - sum([vm.ram_in_gb for vm in self.vms ])
+
+    @property
+    def available_cores(self):
+        return self.usable_cores - sum([vm.cores for vm in self.vms ])
+
 
 class VMProduct(Product):
     vmhost = models.ForeignKey(