Merge pull request #731 in YUNIONIO/onecloud from ~TANGBIN/onecloud:bugfix/tb-capabilities-json-error to release/2.2.0

* commit 'c3a5afd88ea1056a1f05f16fa3460a3e06a59581':
  修复capabilities接口hypervisors为空引发的异常
  修复capabilities接口hypervisors为空引发的异常

pkg/compute/models/capabilities.go

@@ -11,9 +11,9 @@ import (
 )
 
 type SCapabilities struct {
-	Hypervisors        []string
-	StorageTypes       []string
-	GPUModels          []string
+	Hypervisors        []string     `json:",allowempty"`
+	StorageTypes       []string		`json:",allowempty"`
+	GPUModels          []string		`json:",allowempty"`
 	MinNicCount        int
 	MaxNicCount        int
 	MinDataDiskCount   int