Vendor in apitools subset

Pulls in the subset of `apitools` which #334 claims can be used to implement upload / download in `gcloud.storage.key`).  These four modules do not use `google-protorpc` at all.

Updates the vendored-in modules to use relative imports (since they will only be used when the "real"
`apitools` is not available).

Updates our CI configuration to suppress PEP8 / lint checking for the vendored code.
Worth adding `os.path.sep` here? I.E.

```
if filename.startswith(directory + os.path.sep)
```

OTOH, it's not possible AFAIK in posix for have a file named the same as a directory.