Revert "Upgrade ruby to 2.1.2 in bosh release"

This reverts commit a11d4df0a83b29e25c0baf68a4db194ecef5bb64.

Our CentOS image cannot compile Ruby 2.
Clean stemcell-building VM BOSH during provisioning

Signed-off-by: Adam Stegman <astegman@pivotallabs.com>
Lock down bosh_vcloud_cpi dependency

Newer versions can be published independently of BOSH, causing dependency conflicts.

Signed-off-by: Adam Stegman <astegman@pivotallabs.com>