winbind:varlink: Implement get user record by name and uid

winbind:varlink: Implement get user record by name and uid

$> varlink call unix:/run/systemd/userdb/org.samba.winbind/io.systemd.UserDatabase.GetUserRecord "{\"service\":\"org.samba.winbind\",\"userName\":\"AFOREST+user1\",\"uid\":21105}"
{
  "incomplete": false,
  "record": {
    "gid": 20513,
    "homeDirectory": "/home/AFOREST/user1",
    "service": "org.samba.winbind",
    "shell": "/bin/bash",
    "uid": 21105,
    "userName": "AFOREST+user1"
  }
}

Signed-off-by: Samuel Cabrero <scabrero@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>