fix: only configAddons if addons enabled

[jackfrancis]

Reason for Change:

This PR fixes an anomolous invocation of configAddons during CSE, which only exists according to a particular set of conditions. E.g.:

+ time_metric ConfigAddons configAddons
+ local name start end diff tags
+ name=ConfigAddons
+ shift
++ apmz time unixnano
+ start=1582571554614609524
+ configAddons
/opt/azure/containers/provision.sh: line 69: configAddons: command not found

Issue Fixed:

Requirements:

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

Notes:

[jackfrancis]

The new condition in cse_main.sh pairs with this in cse_config.sh:

https://github.com/Azure/aks-engine/blob/master/parts/k8s/cloud-init/artifacts/cse_config.sh#L444

[codecov]

Codecov Report

Merging #2774 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2774   +/-   ##
=======================================
  Coverage   72.35%   72.35%           
=======================================
  Files         137      137           
  Lines       25341    25341           
=======================================
  Hits        18335    18335           
  Misses       5949     5949           
  Partials     1057     1057

[mboersma]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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