Support enable/disable virtual node assignment

[snowch]

Disable:

PUT /api/v1/workers/1 HTTP/1.1
Host: 127.0.0.1:8080
Content-Length: 71
Accept-Encoding: gzip, deflate
REMOTE_ADDR: 86.138.132.112
Accept: */*
User-Agent: python-requests/2.6.0 CPython/2.7.5 Linux/3.10.0-1127.18.2.el7.x86_64
Connection: keep-alive
X-BDS-SESSION: /api/v2/session/46acd825-491e-4e81-95ed-3190bb854a27
Authorization: /api/v2/session/46acd825-491e-4e81-95ed-3190bb854a27

{"operation": "schedule", "id": "/api/v1/workers/1", "schedule": false}

HTTP/1.1 204 No Content
Access-Control-Allow-Origin: *
Content-Length: 0
Content-Type: text/plain
Date: Sun, 02 Aug 2020 09:45:46 GMT
Server: HPE Ezmeral Container Platform 5.1

Enable:

PUT /api/v1/workers/1 HTTP/1.1
Host: 127.0.0.1:8080
Content-Length: 70
Accept-Encoding: gzip, deflate
REMOTE_ADDR: 86.138.132.112
Accept: */*
User-Agent: python-requests/2.6.0 CPython/2.7.5 Linux/3.10.0-1127.18.2.el7.x86_64
Connection: keep-alive
X-BDS-SESSION: /api/v2/session/46acd825-491e-4e81-95ed-3190bb854a27
Authorization: /api/v2/session/46acd825-491e-4e81-95ed-3190bb854a27

{"operation": "schedule", "id": "/api/v1/workers/1", "schedule": true}
HTTP/1.1 204 No Content
Access-Control-Allow-Origin: *
Content-Length: 0
Content-Type: text/plain
Date: Sun, 02 Aug 2020 09:47:03 GMT
Server: HPE Ezmeral Container Platform 5.1

[snowch]

Implement in K8sWorkerProxy and K8sWorker