fix(ec2_securitygroup_not_used): Mock Lambda service

[jfagoagas]

Description

The check ec2_securitygroup_not_used now uses a Lambda service client (#2944) so we need to mock that service client in the check's tests.

I fixed all the Lambda mocks using the same way with the check awslambda_client and created a utils lib with some code that is always present in the tests.

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Merging #2947 (b192d33) into master (54fe10a) will decrease coverage by 0.01%.
Report is 1 commits behind head on master.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2947      +/-   ##
==========================================
- Coverage   86.26%   86.25%   -0.01%     
==========================================
  Files         551      551              
  Lines       17652    17658       +6     
==========================================
+ Hits        15227    15231       +4     
- Misses       2425     2427       +2     

Files	Coverage Δ
...viders/aws/services/awslambda/awslambda_service.py	86.95% <100.00%> (+0.11%)	⬆️
...curitygroup_not_used/ec2_securitygroup_not_used.py	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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[MrCloudSec]

machine 🤖