Use nexus-staging-maven-plugin

The nexus-staging-maven-plugin allows you to deploy to
sonatype, and automatically close and release a repository
without having to log into the sonatype UI. This will allow
us to use sonatype in a CD pipeline.
Use BUSYBOX attribute in SystemTestBase

instead of string "busybox".
Fix and add toJsonString() to CLI responses

Fix misnamed classes in toString().
Add toJsonString() to all CLI responses.
[maven-release-plugin] prepare release 0.8.4
[maven-release-plugin] prepare for next development iteration
Output JSON for `--json` switch in CLI tool

for create, deploy, and undeploy subcommands.
cli: hosts: explicit helios version column

Just VERSION is a bit ambiguous.
Merge pull request #157 from spotify/dano/cli-hosts-explicit-helios-version

cli: hosts: explicit helios version column
Merge pull request #156 from spotify/dxia/more-json-output

Output JSON for `--json` switch in CLI tool
Document helios job file format
Output valid JSON for multi-domain CLI commands