get template info and all kinds of attributes into json dict instead of text

look at the attributes
gongysh@ubuntu64:~/devstack$ tacker vnfd-list
+--------------------------------------+-------+-----------------+--------------+
| id | name | template_source | description |
+--------------------------------------+-------+-----------------+--------------+
| 3f9a2d72-df0a-4545-a853-a52791ff2245 | helod | onboarded | Demo example |
+--------------------------------------+-------+-----------------+--------------+
gongysh@ubuntu64:~/devstack$ tacker vnfd-show helod -c attributes -f json
{
  "attributes": "{\"vnfd\": \"description: Demo example\\nmetadata: {template_name: sample-tosca-vnfd}\\ntopology_template:\\n node_templates:\\n CP1:\\n properties: {anti_spoofing_protection: false, management: true, order: 0}\\n requirements:\\n - virtualLink: {node: VL1}\\n - virtualBinding: {node: VDU1}\\n type: tosca.nodes.nfv.CP.Tacker\\n VDU1:\\n capabilities:\\n nfv_compute:\\n properties: {disk_size: 1 GB, mem_size: 512 MB, num_cpus: 1}\\n properties: {availability_zone: nova, image: cirros, mgmt_driver: noop}\\n type: tosca.nodes.nfv.VDU.Tacker\\n VL1:\\n properties: {network_name: net_mgmt, vendor: Tacker}\\n type: tosca.nodes.nfv.VL\\ntosca_definitions_version: tosca_simple_profile_for_nfv_1_0_0\\n\"}"
}

we should be able to get the attributes value into a json dict, instead of a string.