Integrate gsl-shell/luajit into microbenchmarks

- Also update command to get Julia version info.
- Renames label for gsl-shell/lua tests from gsl_shell to lua.
- Remove non-working external BLAS usage warning

Closes #1662.
Merge pull request #6430 from JuliaLang/cjh/fix-1662

Integrate gsl-shell/luajit into microbenchmarks