feat: add support for Kubernetes 1.15.0-beta.1

[mboersma]

Reason for Change:
See https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG-1.15.md#changelog-since-v1150-alpha3

Issue Fixed:

Requirements:

• Windows artifacts uploaded to acsmirror blob store
• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:
Requires #1369 to merge before this will pass. Merged
CoreDNS was bumped to 1.5.0, but I think this may require configuration changes. I'll take a look at that next.

[codecov]

Codecov Report

Merging #1394 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #1394   +/-   ##
======================================
  Coverage    75.5%   75.5%           
======================================
  Files         128     128           
  Lines       18144   18144           
======================================
  Hits        13700   13700           
  Misses       3641    3641           
  Partials      803     803

[mboersma]

I have the CoreDNS changes ready, but I'd like to separate that into a follow-up PR.

[jackfrancis]

/lgtm

[acs-bot]

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