utils_build

With all the build avoidance fixes, TCs are getting a bit cluttered. As per an idea in https://github.com/autotest/tp-qemu/pull/70 , this pull request adds a utils_build that abstracts much of the building and build avoidance from the test cases.

This is a first version, that does not support e.g. compressed files and autoconf. If needed, it can be updated to support building such projects, but the current scope is just to handle the test applications in virt-test.