Refactoring - Leverage boto3 for Authentication

[vifor2]

PR in response to this issue.
Currently WIP till further feedback/approval.

What has been done :

• Got rid of credentials.py which came from Opinel and by the same move we also got rid of Requests
• Authentification is now made with boto3's Session() instead
• Removed the functionality of using Scout Suite with a CSV (since if you can create one you can also simply modify the .aws/credentials file, which is the standard/documented AWS method)
• Removed the prompt for MFA code since it was only called on one specific case (with roles) and it doesn't really make it easier to use Scout Suite

[codecov-io]

Codecov Report

Merging #215 into develop will increase coverage by 0.51%.
The diff coverage is 31.57%.

@@             Coverage Diff             @@
##           develop     #215      +/-   ##
===========================================
+ Coverage    29.95%   30.47%   +0.51%     
===========================================
  Files           74       73       -1     
  Lines         5428     5067     -361     
===========================================
- Hits          1626     1544      -82     
+ Misses        3802     3523     -279

Impacted Files	Coverage Δ
ScoutSuite/core/cli_parser.py	97.18% <ø> (-0.19%)	⬇️
ScoutSuite/providers/__init__.py	50% <ø> (ø)	⬆️
ScoutSuite/core/console.py	22.22% <ø> (-1.26%)	⬇️
ScoutSuite/providers/aws/profiles.py	32.67% <ø> (-1.88%)	⬇️
ScoutSuite/providers/base/configs/services.py	22.22% <0%> (+1.53%)	⬆️
ScoutSuite/providers/aws/aws.py	17.1% <0%> (ø)	⬆️
ScoutSuite/providers/base/provider.py	10.08% <28.57%> (+0.25%)	⬆️
ScoutSuite/providers/aws/provider.py	10.33% <33.33%> (+0.02%)	⬆️
ScoutSuite/__main__.py	66.3% <50%> (-0.73%)	⬇️
ScoutSuite/output/utils.py	23.68% <0%> (-15.79%)	⬇️
... and 3 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e480f11...1563b9b. Read the comment docs.

[Remi05]

Good job! 👍

[x4v13r64]

Made some changes & tested for:

• Named profile
• No named profile, which reverted to default configured profile
• No named profile or default configured profile, which reverted to credentials configured in environment variables (this should therefore work for EC2/Lambda/ECS)
• GCP/Azure to test integration

README should be updated. It would also be worthwhile to link to https://aws.amazon.com/premiumsupport/knowledge-center/authenticate-mfa-cli/ for MFA configuration.