Centralizes the following images into agnhost:
- dnsutils
- mounttest
- resource-consumer-controller
- test-webserver
Adds CoreDNS to agnhost image, which can be used in some DNS related tests (dnsmasq is Linux-only).
Adds Windows support to mounttest.
Bumps agnhost version to 2.9.
Bumps kitten version to 1.1.
Bumps nautilus version to 1.1.