spec: Add requires from subpackages to libs
    
    Got rpmdiff complaining that the `ostree` and `ostree-tests` packages do
    not have an explicit `Requires` on the libraries. Now, symbol versioning
    assures us that e.g. the -libs version that we pull for a given `ostree`
    package will have the symbols we need, but it doesn't guarantee that
    they'll be the exact same version. Let's add the explicit `Requires` to
    make this clear since in practice we don't want to have to think about
    such mismatches.
    
    I've also taken the opportunity to normalize on the usage of `_isa` and
    `epoch` in all the `Requires`.