Removed micro_bosh_stemcell_path methods

In build.rb & bat_helper.rb
stop syncing micro stemcell bucket
Remove 'micro' from update_light_micro_bosh_ami_pointer_file
Remove concept of stemcell_type from Bosh::Dev::StemcellBuilder
Remove micro stemcell options and rake method
StemcellRakeMethods.build_basic_stemcell becomes build_stemcell.
Fix rubocop issue
Remove code resurrected during merges (#mark_as_latest)
Remove unused spec assets

  * these are now under `bosh-stemcell`
Update name of spec stemcell fixtures (bosh-dev)
Update name of spec stemcell fixtures (bosh-stemcell)
Remove micro from spec descriptions
Use Infrastructure object
Fetch dependencies in initialize, other cleanup
Fix rake's usage of StemcellBuilder