Use BUILD.bazel file when creating py_library rules of extracted whls

[kageiit]

PR Checklist

Please check if your PR fulfills the following requirements:

• Does not include precompiled binaries, eg. .par files. See CONTRIBUTING.md for info
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature (please, look at the "Scope of the project" section in the README.md file)
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Using wheels like keyring (https://pypi.org/project/keyring) , pip_install fails with an error like

  File "/private/var/tmp/_bazel_gkorlam/a1f9cb65ef7d02cf04534e97e406c6b9/external/rules_python/python/pip_install/extract_wheels/lib/bazel.py", line 187, in extract_wheel
    with open(os.path.join(directory, "BUILD"), "w") as build_file:
IsADirectoryError: [Errno 21] Is a directory: 'pypi__keyring/BUILD'

This is because the extracted whl file has a build directory in it.

Issue Number: N/A

What is the new behavior?

By changing the build file to BUILD.bazel it is much less likely to encounter this issue. pip_install succeeds in importing the keyring whl after this change.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[thundergolfer]

👍