test: fix ginkgo failFast

[jadarsie]

Reason for Change:

The way the E2E runner was building the ginkgo command was not gracefully handling empty parameters (in this case failFast)

Related to #3660

Requirements:

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

Notes:

[mboersma]

/lgtm

[jackfrancis]

@jadarsie @haofan-ms thanks for root causing this!

Let's go ahead and change this default to false so we can start running the complete set of tests on all test runs by default:

https://github.com/Azure/aks-engine/blob/master/test/e2e/config/config.go#L50

(Doing so in this PR will also act as a simple smoke test for this fix.)

[codecov]

Codecov Report

Merging #3738 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3738   +/-   ##
=======================================
  Coverage   73.17%   73.17%           
=======================================
  Files         147      147           
  Lines       25322    25322           
=======================================
  Hits        18529    18529           
  Misses       5655     5655           
  Partials     1138     1138           

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[jackfrancis]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis, jadarsie, mboersma

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