docker client pool leak mitigation

Create and tear down the client at each usage.

Back Story: we've seen issues where excessive communication with the docker daemon has left the agent in a stuck state. Upon investigation, it appears that threads are stuck attempting to get connections from the connection pool in the docker client. We dug in some more and cannot figure out why, given the circumstances we see, how the pool would be exhausted. So to avoid the whole thing, we just create clients when we need them, and dispose of them right away.
Upgrade findbugs dep to 3.0.0

This will be needed if we switch to java 8.
agent: syslog: explicitly use image CMD

docker 1.2+ does not implicitly make use of the image CMD if the
ENTRYPOINT has been explicitly set on the container. Therefore, in order
to decorate the ENTRYPOINT, we have to also explicitly copy over the CMD
from the image config to the container config.

https://github.com/docker/docker/pull/6909
https://github.com/docker/docker/issues/7437
Merge pull request #299 from spotify/dano/entrypoint-decoration-fix

agent: syslog: explicitly use image CMD
Merge pull request #298 from spotify/dxia/findbugs-3.0.0

Upgrade findbugs dep to 3.0.0
Upgrade docker-client dep to 2.7.1

This version applies connect timeout to acquiring a connection
Fix tests.
Merge pull request #300 from spotify/dxia/upgrade-docker-client

Upgrade docker-client dep to 2.7.1
Add an end-to-end test for syslog redirection

1. Make the path to syslog used by SyslogRedirectingContainerDecorator
   configurable via the SYSLOG_REDIRECTOR job environment variable.

2. With an image that has a prespecified ENTRYPOINT and CMD, test that
   redirection actually works is sending stdout to the specified endpoint,
   while respecting the command specified in the Dockerfile.
Merge pull request #301 from spotify/rohan/syslog

Add an end-to-end test for syslog redirection
Merge pull request #297 from spotify/drewc/dockerpoolleak

docker client pool leak mitigation
Test that we can deploy a large number of jobs

Deploy 40 jobs, kill all the underlying containers, and make sure the
system recovers.