Set wgGitInfoCacheDirectory to point to scap managed location

Scap populates cache/gitinfo in each deploy branch with pre-computed
information for GitInfo.

Depends on Iceb9e1ce8d3b4bb08f89fa6ec5d5e7392aaafd46.

Bug: 53972
Change-Id: I4bbca69cef8b76bf3f46e14852753faad0a049ee