OpenStack - Ensure inventory is collected for all tenants.

@Fryguy @blomquisg please review.

For OpenStack refresh, ensure inventory is collected for all of the
tenants the EMS can access.

Extended OpenstackHandle to include tenant iterators.
Updated EmsOpenstack and the openstack parser to use the OpenstackHandle accordingly.
Updated spec tests and rerecorded vcr cassettes.
@roliveri I'm concerned about setting this different than our [dynamic value](https://github.com/ManageIQ/manageiq/blob/a0b4744f96c4e730c08a8bbe07a4614e265f5124/vmdb/spec/spec_helper.rb#L93)

@brandondunne @blomquisg thoughts?

I mean, it's annoying to have to know that you should change the value in the spec_helper.rb if there's a travis failure you want to recreate locally but there's obviously a reason @Fryguy changed it globally for the CI environment.