Quite a few images are only used a few times in a few tests. Thus,
the images are being centralized into the agnhost image, reducing
the number of images that have to be pulled and used.
This PR replaces the usage of the following images with agnhost:
- audit-proxy
- crd-conversion-webhook
- entrypoint-tester
- inclusterclient
- iperf
- porter
- serve-hostname
The framework/ssh.go code was heavily used throughout the framework
and could be useful elsewhere but reusing those methods requires
importing all of the framework.
Extracting these methods to their own package for reuse.
Only a few methods had to be copied into this package from the
rest of the framework to avoid an import cycle.
