Merge pull request #73 from theuni/cache

cache: define cache paths and GBUILD_CACHE_ENABLED conditionally
Revert "git: minimize uploaded git files"

This reverts commit dcf28c8b8638d2e83bb4b9ffd15cdb07ad3de249.

due to issue #74 - branches don't work
fix copy-from-target when using lxc to copy a subdir