Assorted cleanup items in the RPM spec file. (#7927)

* Add explicit creation of log and cache directories to specfile. This eliminates a RPM build error seen on multiple OSes with recent versions of rpmbuild. * Change build dependency for RPMs fron `git` to `git-core`. We don't actually need everything the regular `git` package pulls in, just the `git` command and a handful of built-in sub-commands, so we can just depend on `git-core` during the build instead of the full package. This causes no issues for existing build workflows, as `git` pulls in `git-core`. However, it will allow us to make the new Docker-based package building workflow a bit more efficient as we can decrease the size of the package builder images. * Remove useless build dependency on netcat in specfile. We don't actually use netcat anywhere during the build process, so there's no point in depending on it for the build. * Update RPM specfile changelog.