Remove experimental incremental stemcell code

Signed-off-by: Colin Humphreys <chumphreys@pivotallabs.com>
Simplify bash code to prep for ruby conversion

Signed-off-by: Colin Humphreys <chumphreys@pivotallabs.com>
Remove non-vSphere centos spec files

Signed-off-by: Colin Humphreys <chumphreys@pivotallabs.com>
Remove logic from stemcell spec files

Signed-off-by: Colin Humphreys <chumphreys@pivotallabs.com>