retry 401s from the envoy

[djk121]

Because there can be enough time between when _is_enphase_token_expired()
is called and when the subsequent http request to the envoy happens,
the token freshness check can pass but the envoy will still see an
expired token. This results in a 401 from the envoy, which raises
an exception.

This change looks for these 401s and attempts to refresh the
token twice before giving up.

Pull request recommendations:

• Name your pull request your-development-type/short-description. Ex: feature/read-tiff-files
• Link to any relevant issue in the PR description. Ex: Resolves [Improve library and HA integration to reduce number of HTTP calls to Envoy device #12], adds tiff file format support
• Provide context of changes.
• Provide relevant tests for your feature or bug fix.
• Provide or update documentation for any feature added by your pull request.

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