Simplify local reproduction instructions
Ok, this is ready for review again. I fixed a few issues, including one bug with including TFCI variables from the environment, and added more documentation -- mostly about docker. I have verified that (on my Linux machine), these all appeared to be working:

- local_multicache
- local_rbe
- local_nodocker
- pycpp.sh
- any.sh
- wheel.sh

I don't have a good way to verify bisect.sh yet but I think it's fixed. I'll check on it again after this gets merged.
This change is a big simplification of reproducing a build locally ([see it here](https://github.com/angerson/tensorflow/tree/master/ci/official)):

- Moved a lot of configurable behavior into source-able local_* env files
- Deleted a lot of extraneous instructions
- Added "how do I choose..." instructions for clarification
- Fixed a bug preventing multiple invocations of rename_and_verify_wheels
- Made any.sh and bisect.sh use the cleaner method of sourcing local_ envs
- Cleaned up ci_default and added "how to see an overview of env variables"

One of the big things is that I added some logic in local_default that resets the list of Bazel common args to remove things like --config=rbe. This way a user can choose to run a "release" env configuration without being blocked by permission errors, or by needing to manually amend their configuration. As a result, gathering the correct set of config values is quite easy (see the new instructions). The alternative would be to split "auth-related" flags into a separate variable, which I don't like, as I think it's more confusing for future maintainers to have to continuously decide which options go where.