Generifies the stemcell filename used in setup director
Generifies the stemcell filename used in setup director

Setup-director needs to use a more generic dirglob pattern to match stemcells
that look like stemcell.tgz or china-light-stemcell.2.3.4.other-stuff.tgz
depending on the resource input of stemcell since in some cases they use a
stemcell from an s3 resource and in others they use a bosh-io-stemcell

[#106769460](https://www.pivotaltracker.com/story/show/106769460)

Signed-off-by: Jonathan Barnes <bc7add126c2dbb8382bf1c28ac262b9363a32706@pivotal.io>

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