Remove explicitly set ELB name
Remove explicitly set ELB name

- A fixed name prevented creation of two stacks in parallel
- AWS will generate a unique name if one is not provided

[#113005251](https://www.pivotaltracker.com/story/show/113005251)

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