be more explicit about pipeline artifacts archive filename testing

Signed-off-by: dmitriy kalinin <dmitriy@pivotallabs.com>
refactor PipelineArtifacts in preparation for vsphere centos stemcell promotion

Signed-off-by: dmitriy kalinin <dmitriy@pivotallabs.com>
added vsphere centos pipeline artifact

Signed-off-by: dmitriy kalinin <dmitriy@pivotallabs.com>
removed unneeded namespace in PipelineArtifacts

Signed-off-by: dmitriy kalinin <dmitriy@pivotallabs.com>
formatting

Signed-off-by: dmitriy kalinin <dmitriy@pivotallabs.com>
removed Infrastructure.all method

Signed-off-by: dmitriy kalinin <dmitriy@pivotallabs.com>