cli/client: default to http registration

Default to http service registration instead of hermes. This will not
affect existing jobs.
Merge pull request #32 from spotify/dano/default-http-registration

cli/client: default to http registration
[maven-release-plugin] prepare release 0.0.29
[maven-release-plugin] prepare for next development iteration
cli: hosts: print docker x.yy.zzz version only

The cli currently prints something like:

DockerVersion{apiVersion=1.12, arch=amd64, gitCommit=688b5cf-dirty, 
goVersion=go1.2.1, kernelVersion=3.13.0-24-generic, os=linux, 
version=1.0.0} (1.12)

We want something like: 1.0.0 (1.12)
master/agent: fast shut down using SIGKILL

* There's no state that must be persisted.
* Let the kernel deal with closing sockets etc.
* Let zookeeper figure out that the agent is gone.
cli: undeploy: -f/--force flag

The -f/--force flag together with -a/-aal causes the job to immediately
be undeployed everywhere without any prompting.
Merge pull request #37 from spotify/dano/cli-undeploy-force

cli: undeploy: -f/--force flag
zk updater: handle retry failures

On NodeExists and NoNode failures, assume that we're out of sync and
resync, with exponential backoff.
Merge pull request #34 from spotify/dano/cli-fix-hosts-docker-version

cli: hosts: print docker x.yy.zzz version only
do not run zk updater tests in parallel

Avoid spawning a lot of sub processes, which makes
travis sad.
[maven-release-plugin] prepare release 0.0.30
[maven-release-plugin] prepare for next development iteration
Merge pull request #36 from spotify/dano/shutdown-sigkill

master/agent: fast shut down using SIGKILL
cli: less verbose duration formatting
Merge pull request #40 from spotify/dano/cli-less-verbose-duration-format

cli: less verbose duration formatting
Merge pull request #39 from spotify/dano/zk-updater-handle-retry-conflicts

zk updater: handle retry failures
Merge pull request #38 from spotify/dano/zk-updater-test-no-parallel

do not run zk updater tests in parallel
sys test: teardown: do not assume setup succeeded

If setup fails before zk was assigned, teardown would NPE.
move docker probing to system test

Fail faster when docker is down/unreachable.