Extract `bosh-common` to a separate repository and replace `bosh_common` globally

[aramprice]

1. Normalize ruby name-spacing in bosh common code

• Extract bosh-template to bosh-common #2608

2. Extract bosh-common to its own repository

• Add repo for bosh-common community#1157

4. Update all Ruby-based CPI's to consume bosh-common instead of bosh_common

• https://github.com/cloudfoundry/bosh-azure-cpi-release/
• https://github.com/cloudfoundry/bosh-openstack-cpi-release/
• https://github.com/cloudfoundry/bosh-aws-cpi-release/

5. Update https://github.com/cloudfoundry/docs-bosh
6. Other bosh_common replacements