Use environment variables instead of -a and -p dog options

If I bind sheep daemon to a specific ip (-b <ip>), then I have to use options -a and -p options each time I run dog

E.g.

dog node list
failed to connect to 127.0.0.1:7000: Connection refused
failed to connect to 127.0.0.1:7000: Connection refused
Failed to get node list

dog node list -a 192.168.2.68 -p 7000
  Id Host:Port V-Nodes Zone
   0 192.168.2.68:7000 128 1141024960
   1 192.168.2.69:7000 128 1157802176
   2 192.168.2.71:7000 128 1191356608

Using environment variables would simplify dog syntax.