heat-cfn : Make error with missing auth details more obvious

Exit with an error message describing the missing auth details
instead of failing with cryptic "Name or service not known" error
when credentials etc are missing

fixes bug #1154759

Change-Id: I19c22357526c73e824a2b2bb9f862c8724a8ebba
Merge "heat-cfn : Make error with missing auth details more obvious"