Don't automatically create `-data` containers

[wallrj]

gear install creates a -data container for each of its units if one doesn't already exist.

It would be tidier if gear only used the --volumes-from argument if a -data container was found.

This would avoid leaving behind unused -data containers when stateless units are deleted.

Not sure if it's possible to do such a test in the systemd service file, but perhaps the service files would be cleaner if they called a gear wrapper script to launch docker containers and move the various container tests into that script.

See

• Removing a gear unit leaves behind a <myunitname>-data container ClusterHQ/flocker#409

$ sudo gear install openshift/busybox-http-app:latest my-unit

$ sudo gear list-units -a
ID      SERVER  ACTIVE  SUB     LOAD    TYPE
my-unit         active  running loaded  

$ docker ps -a
CONTAINER ID        IMAGE                               COMMAND                CREATED             STATUS                   PORTS               NAMES
a8360222d9a0        openshift/busybox-http-app:latest   /opt/sti/run           2 hours ago         Up 2 hours               8080/tcp            my-unit             
bed17b6bf149        openshift/busybox-http-app:latest   /bin/true /opt/sti/r   2 hours ago         Exited (0) 2 hours ago                       my-unit-data  

$ sudo gear stop my-unit
Aug 19 05:58:00 localhost.localdomain systemd[1]: Stopping Container my-unit...
Aug 19 05:58:00 localhost.localdomain docker[17573]: my-unit
alter_container_state: Stop job done
journal: Done
Container my-unit is stopped

$ docker ps -a
CONTAINER ID        IMAGE                               COMMAND                CREATED             STATUS                   PORTS               NAMES
bed17b6bf149        openshift/busybox-http-app:latest   /bin/true /opt/sti/r   2 hours ago         Exited (0) 2 hours ago                       my-unit-data        

$ sudo gear delete my-unit
Deleted my-unit

$ docker ps -a
CONTAINER ID        IMAGE                               COMMAND                CREATED             STATUS                   PORTS               NAMES
bed17b6bf149        openshift/busybox-http-app:latest   /bin/true /opt/sti/r   2 hours ago         Exited (0) 2 hours ago                       my-unit-data       

$ sudo gear clean
INFO: 2014/08/19 05:59:54 --- "FAILED CONTAINERS" CLEANUP ---
INFO: 2014/08/19 05:59:54 --- HOME DIRECTORY REPAIR ---
INFO: 2014/08/19 05:59:54 --- PORTS CLEANUP ---

$ docker ps -a
CONTAINER ID        IMAGE                               COMMAND                CREATED             STATUS                   PORTS               NAMES
bed17b6bf149        openshift/busybox-http-app:latest   /bin/true /opt/sti/r   2 hours ago         Exited (0) 2 hours ago                       my-unit-data        

[smarterclayton]

I had started down this road in #198 - providing a better wrapper. I don't think there's much left to bring it up to speed - the isolation mode was problematic for various reasons (would be better prototyped in Docker directly), but the rest was working.