restore exechealthz defs for back compat

[mboersma]

What this PR does / why we need it:
AKS using acs-engine had a malformed image tag with the healthz container in kube-dns for 1.11.1:

  healthz:
    Container ID:
    Image:         k8s.gcr.io/
    Image ID:
    Port:          8080/TCP
    Args:
      --cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1 >/dev/null
      --url=/healthz-dnsmasq
      --cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1:10053 >/dev/null
      --url=/healthz-kubedns
      --port=8080
      --quiet

I think #3595 didn't go far enough, so this adds the exechealthz def to 1.11 and 1.12.

If applicable:

• documentation
• unit tests
• tested backward compatibility (ie. deploy with previous version, upgrade with this branch)

Release note:

restore exechealthz defs for back compat to 1.11 and 1.12

[codecov]

Codecov Report

Merging #3620 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3620      +/-   ##
==========================================
+ Coverage    55.5%   55.51%   +<.01%     
==========================================
  Files         107      107              
  Lines       16194    16196       +2     
==========================================
+ Hits         8989     8991       +2     
  Misses       6432     6432              
  Partials      773      773

[jackfrancis]

/lgtm

[acs-bot]

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