Do not install build and .git directories for lhcbpr tests

@rmatev proposed to save some time of unzipping in lbn-install for LHCbPR tests by skipping the installation of the build directory. We probably also do not need the .git directory (@clemenci do we need it for nightly tests?).

Since this may be a disruptive change for other LHCbPR tests (most notably for Gauss), the plan is to announce it on this Wednesday's Core Software meeting and ask people to watch out for failures after it's merged.

/cc @dpopov