fix up create / pull retries
fix up create / pull retries

passing a context to create didn't seem to overwrite the underlying client
timeout (boo) -- we should probably modify fsouza in the near future. so made
2 clients, one with a long timeout that we need to use for pull as well.
basically made up a number, but create has taken 7 minutes and actually worked
so I figure 30 minutes will avoid spurious timeouts. setting this threshold
over 10 minutes means that it won't be retried at all -- I think this is ok.

this and the last commit fixes the 'no such container' bug in start and no
logs bug from the same issue when attaching -- there's added logic for this
all to fall out now, too.

this also twiddles some various http client knobs that we normally twiddle,
which should help performance a little -- we're likely churning through a lot
of connections at the moment, specifically.

iron-io/runner,iron-io/runner