remove docker inspect container

we had the inspect container here for 3 reasons:

1) get exit code
2) see if container is still running (debugging madness)
3) see if docker thinks it was an OOM

1) is something wait returns, but due to 2) and 3) we just delayed it until
inspection

2) was really just for debugging since we had 3)

3) seems unnecessary. to me, an OOM is an OOM is an OOM. so why have a whole
docker inspect call just to find out? (we could move this down, since it's a
sad path, and make the call only when necessary, but are we really getting any
value from this distinction anyway? i've never ran into it, myself)

inspect was actually causing tasks to time out, since the call to inspect
could put us over our task timeout, even though our container ran to
completion. we could have fixed this by checking the context earlier, but we
don't really need inspect either, which will reduce the docker calls we make,
which will make more unicorn puppers. now tasks should have more 'true'
timeouts.

tried to boy scout, but tracing patch also cleans this block up too.

api/runner/drivers/docker/docker_client.go

@@ -36,7 +36,6 @@ type dockerClient interface {
 	RemoveContainer(opts docker.RemoveContainerOptions) error
 	PullImage(opts docker.PullImageOptions, auth docker.AuthConfiguration) error
 	InspectImage(name string) (*docker.Image, error)
-	InspectContainer(id string) (*docker.Container, error)
 	Stats(opts docker.StatsOptions) error
 }
 
@@ -270,16 +269,6 @@ func (d *dockerWrap) InspectImage(name string) (i *docker.Image, err error) {
 	return i, err
 }
 
-func (d *dockerWrap) InspectContainer(id string) (c *docker.Container, err error) {
-	ctx, cancel := context.WithTimeout(context.Background(), retryTimeout)
-	defer cancel()
-	err = d.retry(ctx, func() error {
-		c, err = d.docker.InspectContainer(id)
-		return err
-	})
-	return c, err
-}
-
 func (d *dockerWrap) Stats(opts docker.StatsOptions) (err error) {
 	// we can't retry this one this way since the callee closes the
 	// stats chan, need a fancier retry mechanism where we can swap out