Add BigCouch/ES maintenance scripts on central (refs #7738)

* Add scripts to backup, restore, and compact BigCouch databases
* Add Elasticsearch heap stats script
* Share install_ruby_tools.sh across multiple roles
* Add gems needed for BigCouch restore script via script
* Install rbenv and bundler on central
Merge pull request #22 from dpla/7738-add-missing-scripts

Add BigCouch/Elasticsearch maintenance scripts (refs #7738)