test: use AZURE_CORE_ONLY_SHOW_ERRORS when running E2E

[jackfrancis]

Reason for Change:

This PR ensures that any usage of the E2E test runner invoked az with the suppression of non-error output.

See:

https://github.com/Azure/azure-cli/blob/dev/src/azure-cli-core/HISTORY.rst#230

Also, two tweaks to the vmss-prototype tests based on observations:

• If we're configured to test the vmss-prototype functionality, we automatically set RunUnattendedUpgradesOnBootstrap to false in the LinuxProfile
• retry the kured daemonset creation

Issue Fixed:

Credit Where Due:

Does this change contain code from or inspired by another project?

• No
• Yes

If "Yes," did you notify that project's maintainers and provide attribution?

• No
• Yes

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis

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[codecov]

Codecov Report

Merging #4288 (3b57385) into master (c252387) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4288      +/-   ##
==========================================
+ Coverage   72.02%   72.03%   +0.01%     
==========================================
  Files         141      141              
  Lines       21625    21633       +8     
==========================================
+ Hits        15576    15584       +8     
  Misses       5099     5099              
  Partials      950      950              

Impacted Files	Coverage Δ
pkg/api/common/versions.go	96.37% <0.00%> (ø)
pkg/api/vlabs/validate.go	81.46% <0.00%> (+0.03%)	⬆️
pkg/armhelpers/mockclients.go	25.05% <0.00%> (+0.99%)	⬆️

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