Work-around missing Git repository during Tox runs
Work-around missing Git repository during Tox runs

The changes introduced in 00a95a87 broke `tox` runs because these rely
on source packages. This commit works around by supporting non-Git
trees, setting the version to '999' unconditionally.

See: 00a95a87cee314fe25df41dc039dc09de794a91f

scality/ScalitySproxydSwift,scality/ScalitySproxydSwift