Upgrade ruby to 2.1.2 in bosh release

Signed-off-by: Adam Stegman <astegman@pivotallabs.com>
Lock down json gem version in bosh release

Without explicit versioning bundler attempts to use system json which
doesn't exist in our gem_home resulting in a undefined method
`source_uri' error

* Update GEM_HOME in bosh release jobs start scripts

Signed-off-by: Maria Shaldibina <mshaldibina@pivotal.io>