Use more resilient way to find ruby versions to update to
Use more resilient way to find ruby versions to update to

[#158896087](https://www.pivotaltracker.com/story/show/158896087)

Co-authored-by: David Ansari <1fc10f46b774f6939d18bebc734f673f94104821@sap.com>

cloudfoundry-incubator/bosh-openstack-cpi-release,cloudfoundry-incubator/bosh-openstack-cpi-release,cloudfoundry-incubator/bosh-openstack-cpi-release