Update README with vagrant-vbguest prerequisite

This removes the instructions for remounting directories after a
kernel upgrade.

See https://issues.dp.la/issues/7713
Add missing tags to dbnode tasks
Add bigdesk plugin to Elasticsearch
Add playbook for central server

This server is for cloud environments (not development) and is
independent of staging, production, and contentqa.  It has its
own inventory file, "central".

Modify the common role's hosts.j2 template so that it will work
without a level (environment) being specified.
Add loadbalancer management for staging, production

- Add README note about new Python module dependency
- Add new vars, pre and post tasks for dbnode role
- Add pre and post tasks to Elasticsearch playbook
- Add loadbalancer tasks to API playbook
- Add loadbalancer tasks for site proxy
  Also move siteproxy plays to their own playbook.

Plus improvements to Elasticsearch restart behavior:
- Set Elasticsearch unicast hosts array
  This seems to help avoid split-brain syndrome.
  It also makes node discovery a lot faster.
- Add shard replcation toggling for Elasticsearch
  Before Elasticsearch nodes are restarted, and before we do
  anything that might cause one of them to fail to come back
  up, we disable shard reallocation to keep the cluster from
  transferring huge shard files when it thinks one of the nodes
  has gone down.
Rearrange and add playbooks for greater convenience

New playbooks have been added for executing tasks confined to a
specific role.  Some, like "common," have been broken out to allow
for this.  Some have been modified to allow them to be run
standalone.
Have contentqa_all.yml include new common playbook
Add playbook to initialize new development environment

Also add prerequisite for the httplib2 Python module.
Fix variable inclusion, common.yml playbook
Break out common httpd into separate playbook
Fix repo initialization script

Fix ruby version not being passed to script that creates api key
database.
Fix database name 'bulk_download' in repo init playbook

It was incorrectly defined as 'bulk_downloads'.
Add ntp to common packages
Add production playbook, fix loadbalancer issues

- Add production playbook.
- Add conditions and advice in comments for initial setup in a
  cloud environment with loadbalancers.
Add example variable api_branch_or_tag to file

Add to roles/api/vars/development.yml.dist
Update required Ansible version in README
Add missing parameter to ansible-playbook invocation

Add the necessary --extra-vars parameter to the instructions for
performing an installation.  The initial_run=true setting is
necessary to avoid a failure in the ElasticSearch setup.
Remove outdated comment from Vagrantfile.dist
Add usage comment to dev_all.yml playbook

This is related to commit d04827eeb64
Fix typo in playbook