Upgrade fails from 1.15.7 to 1.16.4

[Tamas Ecsedi]

Describe the bug
Upgrade fails with:

  err> [preflight] Some fatal errors occurred:
  err> 	[ERROR CoreDNSUnsupportedPlugins]: there are unsupported plugins in the CoreDNS Corefile

Steps to reproduce the issue:

pke upgrade master --kuberentes-version=1.16.4

Expected behavior
Upgrade succeeds.

Additional context
See related issue in Kubernetes: kubernetes/kubernetes#82889