Implement AuthN handling in Master for the Scheduler endpoint

$ cat /tmp/subscribe-943257503176798091.bin | http --print=HhBb --stream --pretty=colors --auth verification:password1 POST :5050/api/v1/scheduler Accept:application/x-protobuf Content-Type:application/x-protobuf
POST /api/v1/scheduler HTTP/1.1
Connection: keep-alive
Content-Type: application/x-protobuf
Accept-Encoding: gzip, deflate
Accept: application/x-protobuf
Content-Length: 126
User-Agent: HTTPie/0.9.0
Host: localhost:5050
Authorization: Basic dmVyaWZpY2F0aW9uOnBhc3N3b3JkMQ==



+-----------------------------------------+
| NOTE: binary data not shown in terminal |
+-----------------------------------------+

HTTP/1.1 401 Unauthorized
Date: Fri, 13 Nov 2015 20:00:45 GMT
WWW-authenticate: Basic realm="Mesos master"
Content-Length: 65

HTTP schedulers are not supported when authentication is required