Large initial time taken for `kraft build`

[razvand]

Describe the bug

When running kraft build for the first time for a given application (such as app-micropython) (after running kraft configure), it takes some time (about 1-2 minutes). Everything else goes smooth. This has only recently happened.

Subsequent calls to kraft build are fine. However, if kraft clean -p is issued (cleaning the build/ folder), kraft build once again takes some time. I was able to replicate this on multiple systems.

I don't recall this being the case before. Maybe it's because of the recent update to the build system.

To Reproduce

Build any Unikraft application using kraft: setup environment, use kraft configure then kraft build. I used app-micropython to test this.

Expected behavior

kraft build should run faster.

Desktop (please complete the following information):

• OS: Linux
• Version: Ubuntu 18.04, Debian 10