Bump vcap_common to 4.0.1

This version of vcap_common locks down the cookiejar dependency to 0.3.0.
The em-http-request dependency of vcap_common requires this version to
function correctly.

[#65300526]
Add actor_name and actee_name field descriptions to API spec.

[#66200550] and [#66199904]
Remove buildpacks with null urls