[atomic] Revisiting the defaults for `atomic run` with and without --spc #75

["Brian (bex) Exelbierd" <bexelbie redhat com>]

I've opened issue #75: https://github.com/projectatomic/atomic/issues/75

The current default behavior is inconsistent for SPC and non-SPC 
invocations (see below).

In short, the default for `atomic run --spc` drops you into an 
interactive session.  The default for `atomic run` is to create a 
running container that can later be used for commands.

PR #74 fixes this behavior.

However, I'd like us to rethink this.  I believe a better solution would 
be something like this:

`atomic run [--spc] image [command]`:
    if (CREATE LABEL present)
      execute CREATE label passing command if present in an environment 
variable
    if (RUN LABEL present)
      execute RUN LABEL passing command if present in an environment 
variable
    else
        use `docker create` to launch the container and then `docker 
exec` with /bin/bash or command if present

`atomic start [--spc] image [command]`:
    if (CREATE LABEL present)
      execute CREATE label passing command if present in an environment 
variable
    else
        use `docker create` to launch the container passing command if 
present


--------------------------------------------------------------------------------
Example of current behavior
--------------------------------------------------------------------------------
# ./atomic run --spc busybox /bin/ps
Container 'busybox-spc' must be running before executing a command into it.
Execute the following to create the container:
./atomic run --spc --name busybox-spc busybox
# ./atomic run --spc busybox
/usr/bin/docker run -t -i --rm --privileged -v /:/host -v /run:/run -v 
/etc/localtime:/etc/localtime --net=host --ipc=host --pid=host -e 
HOST=/host -e NAME=${NAME} -e IMAGE=${IMAGE} ${IMAGE} /bin/sh
<interactive shell>
--------------------------------------------------------------------------------
# ./atomic run busybox /bin/ps
Container 'busybox' must be running before executing a command into it.
Execute the following to create the container:
./atomic run busybox
# ./atomic run busybox
/usr/bin/docker create -t -i --name ${NAME} ${IMAGE} /bin/sh
busybox
# docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED 
        STATUS              PORTS               NAMES
e7f88fef782d        busybox:latest      "/bin/sh"           5 seconds 
ago       Up 4 seconds                            busybox

regards,

bex