Adds support for backups via snapshot API

Fixes https://github.com/rackspace-cookbooks/elkstack/pull/45.
Lint fixes
Cleanup agent to use enabled flag everywhere
Still allow nil to enable logging
Cleanup logging flag for agent
ES 1.3.4 has been released and contains only minor bugfixes. Setting as default version
Check for logstash basedir and error nicely

Fixes https://github.com/rackspace-cookbooks/elkstack/issues/64
Fix rubocop line too long
Version bump
Adds support for backups via snapshot API

Fixes https://github.com/rackspace-cookbooks/elkstack/pull/45.
Merge with upstream/master
Fix rubocop and merge error too
Merge pull request #61 from martinb3/cloud_files_backup2

Adds support for backups via snapshot API