Bugfix/1568 bucket enumeration failure oci

[WhiteThePanda]

Description

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Ran against OCI tenancies, the tool could not proprely parse the namespace of the tenancy for bucket retrieval.
I think the issue was due to the problem addressed by this comment in the code, when retrieving the namespace from the API:
" # for some reason it returns a list of chars instead of a string"
I guess the response of the API on OCI's side has changed and the namespace is now retrieved as a whole string. Code was updated in consequence to make adequate use of the API.

Fixes #1568

Type of change

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works (optional)
• New and existing unit tests pass locally with my changes

(Sorry, this is my first pull-request ever in my life and I am not sure on how to use the tests (I am only using OCI), I have verified my work by running the tool with my personal credentials)