Remove dockerclient

This is no longer needed now we have dockerserver.

Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Rename forward backend to dockerclient

Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Remove dockerclient heartbeat

Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Tests for dockerclient

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>
Merge pull request #85 from bfirsh/rename-forward-to-dockerclient