Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Fix pkg_rpm rules for bazel 0.13+

**What this PR does / why we need it**: next step in addressing https://github.com/kubernetes/kubernetes/issues/63108; we can use the substitutions supported by bazel 0.13+ to get the `pkg_rpm` rules to work properly again.

I've also added a filegroup to allow building all of the RPMs easily with `bazel build //build/rpms`. Note that since these are manual, `bazel build //...` will still skip building them. 

**Release note**:

```release-note
NONE
```

/assign @BenTheElder 
cc @sigma