Implement pause/unpause commands

[vdemeester]

Implementing pause and unpause commands from docker-compose. Part of #124 🐙.

$ libcompose-cli ps
WARN[0000] Note: This is an experimental alternate implementation of the Compose CLI (https://github.com/docker/compose) 
Name                             Command  State         Ports
multiple-composefiles_another_1  top      Up 3 seconds  
multiple-composefiles_simple_1   top      Up 3 seconds 

$ libcompose-cli pause
$ libcompose-cli ps
WARN[0000] Note: This is an experimental alternate implementation of the Compose CLI (https://github.com/docker/compose) 
Name                             Command  State                   Ports
multiple-composefiles_simple_1   top      Up 49 seconds (Paused)  
multiple-composefiles_another_1  top      Up 49 seconds (Paused) 

$ libcompose-cli unpause
$ libcompose-cli ps
WARN[0000] Note: This is an experimental alternate implementation of the Compose CLI (https://github.com/docker/compose) 
Name                             Command  State              Ports
multiple-composefiles_another_1  top      Up About a minute  
multiple-composefiles_simple_1   top      Up About a minute 

Just like for docker-compose, issuing multiple times pause or trying to un-pause a non-paused container won't fail, it just won't do anything. Some integration tests reflect that.

🐸

Signed-off-by: Vincent Demeester vincent@sbr.pm

[vdemeester]

As commented, this is to make sure we won't fail in TearDown because of a paused container… So we're trying to unpause all of them and move on 😉.

[vdemeester]

/ping @dnephin @ibuildthecloud

[dnephin]

LGTM