Beginning a script to backup riak for upgrade

[#74074550]
Add next test and refactor fixtures
Use different responses for fetching service instances of space-0 and space-1
riak-backup script fetches bound apps for service instances and stores their data in metadata.yml
riak-backup script: ignore non-riak service instances

Fetching service instances now uses space summary endpoint instead of
/v2/service_instances/:guid. This makes it easier to get associated service plans
and service models.
riak-backup: add metadata tests for instances with no bound apps
riak-backup: Allow for pagination
riak_backup: name space directories using space name instead of guid
riak_backup: clearer service instance guid names in test suite
riak_backup: service instance directory names are service instance names

instead of guids, which they were previously
riak-backup: script calls FetchBucket for each bucket
riak_backup: space, instance, and binding info now fetched from cf

CfClient implements CfClientInterface
riak_backup: saves contents of bucket to backup data directory
riak_backup: exit if s3cmd is not installed
riak_backup: only create directories for orgs/spaces that have instances

change path of download directory to include org name and space name
riak_backup: backup destination directory is a commandline param
riak_backup: remove the option to restore a backup
riak_backup: print progress output while backing up.
riak-backup: Add readme file
riak-backup: Add link to s3cmd docs in readme