Fix Dummy CPI to use random stemcell IDs
Fix Dummy CPI to use random stemcell IDs

Previously causing issues when testing multi-CPI with shared names

[#154350422](https://www.pivotaltracker.com/story/show/154350422)

Signed-off-by: Luan Santos <509a85c757dc22c0257f4655fb3fb682d42f965b@pivotal.io>
Signed-off-by: Danny Berger <8efccf38e9d8f361e1973ad644e1b1e50ad8ecfe@pivotal.io>

barthy1/bosh,barthy1/bosh,barthy1/bosh,barthy1/bosh