Bug description

Logs in imagebuild will be cleaned up on prebuild page once it fails, and then left a blank log for users.

We should left fail logs here to let users know that what is the reason that build failed.

Steps to reproduce

• Create a repo that with a wrong .gitpod.Dockerfile and set it as image in .gitpod.yml
• Open repo with gitpod, this will show imagebuild failed
• Create a project for this repo
• Open repo with gitpod, this will show prebuild failed

And logs of imagebuild will be cleaned up after it failed