Upgrade fog gem to latest

 * manual merge of pr/365 "Upgrade fog gem to v1.14.0"
Add rubocop as spec:unit dependency

 * this should improve pull requests as more people will run rubocop
Move stemcell create command out of rake
Extract StemcellBuilder (boundary object)
StemcellEnvironment no longer knows about builder
Move sanitize out of rake into tested ruby object
Extract publishing out of stemcell environment
Instantiate pipeline once to make it injectable
Remove redundant requires
[openstack_cpi] Retry on OpenStack API InternalServer errors