new call wrappers for limits, quota-sets, tenant-usage and hypervisors

This pull request contains two commits for the functionality describe in the title.
`required: false` and other similar code need to be converted to the hashrocket style `:required => false` since the former does not work with Ruby 1.8. Personally, I'd rather use the newstyle but since other projects still need to use this library with Ruby 1.8 (e.g. Puppet), I need to accommodate them.