add option to not require setup/teardown the service every call

[s4ke]

Add two new commands:

Something along the lines of

docker swarmproxy setup --service-name "docker_swarm_proxy" --network-name "network-name"

docker swarmproxy teardown --service-name "docker_swarm_proxy" --network-name "network-name"

Then, add the option to specify the same on the actual exec command:

docker swarmproxy service exec --service-name "docker_swarm_proxy" --network-name "network-name" ...