Fix deleteinstance command line function

[giovannt0]

Fix #273

• Fix attribute selection from argparser
• Fix try/except block catching the wrong exception. When delete_all_disks is True, the library will try to delete the disk that has already been deleted by the instance delete operation, thus throwing a ResourceNotFoundError error.

~/(venv) giovannt0@: cloudforensics gcp <project_id> deleteinstance instance-1 --delete_all_disks
[2020-12-17 14:31:25,239] [libcloudforensics.providers.gcp.internal.compute] INFO     project:<project_id> Deleting Instance: instance-1
[2020-12-17 14:31:43,852] [libcloudforensics.providers.gcp.internal.compute] ERROR    Disk instance-1 was not found in project <project_id>
[2020-12-17 14:31:43,852] [libcloudforensics.providers.gcp.internal.compute] INFO     project:<project_id> Could not find disk: instance-1, skipping
Instance deleted.

Despite the logging, the instance and its disk are now deleted as expected. Alternatively we could filter out already deleted disks from the disks_to_delete list to prevent ResourceNotFoundError from being thrown in the first place.

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[giovannt0]

@googlebot I signed it!

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[hacktobeer]

And have a lovely Christmas/NYE Theo!

[giovannt0]

Thank you @hacktobeer, you as well!

[codecov-io]

Codecov Report

Merging #274 (a817e9a) into master (e4448c6) will increase coverage by 0.63%. The diff coverage is 67.89%.

@@            Coverage Diff             @@
##           master     #274      +/-   ##
==========================================
+ Coverage   65.39%   66.03%   +0.63%     
==========================================
  Files          14       29      +15     
  Lines         968     2102    +1134     
==========================================
+ Hits          633     1388     +755     
- Misses        335      714     +379     

Flag	Coverage Δ
nosetests	66.03% <67.89%> (+0.63%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...cloudforensics/providers/azure/internal/network.py	24.52% <24.52%> (ø)
libcloudforensics/providers/gcp/forensics.py	40.20% <33.33%> (-24.80%)	:arrow_down:
libcloudforensics/providers/aws/internal/kms.py	40.00% <40.00%> (ø)
...ibcloudforensics/providers/gcp/internal/compute.py	53.97% <50.77%> (-8.39%)	:arrow_down:
libcloudforensics/providers/aws/forensics.py	56.16% <53.06%> (-13.61%)	:arrow_down:
...cs/providers/gcp/internal/compute_base_resource.py	37.33% <54.28%> (+0.82%)	:arrow_up:
libcloudforensics/providers/aws/internal/log.py	73.07% <55.55%> (-4.20%)	:arrow_down:
libcloudforensics/providers/gcp/internal/common.py	56.89% <57.44%> (+0.57%)	:arrow_up:
...bcloudforensics/providers/gcp/internal/function.py	40.54% <62.50%> (+8.28%)	:arrow_up:
...loudforensics/providers/azure/internal/resource.py	65.38% <65.38%> (ø)
... and 35 more

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