test: Adjust SSH fingerprint parsing for RHEL 8.3 OpenSSH
test: Adjust SSH fingerprint parsing for RHEL 8.3 OpenSSH

The fingerprint prompt is now "SHA256 Fingerprint (ecdsa-sha2-nistp256)"
without the "ssh-" prefix, and a more detailed algorithm. Make the ssh-
prefix optional and only take the first part of the algorithm, so that
this gets along with either format.

Closes #14242
deryni/cockpit,mvollmer/cockpit,garrett/cockpit,moraleslazaro/cockpit,deryni/cockpit,martinpitt/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,deryni/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,deryni/cockpit,moraleslazaro/cockpit,deryni/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,garrett/cockpit,moraleslazaro/cockpit,garrett/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,garrett/cockpit,cockpit-project/cockpit,garrett/cockpit,martinpitt/cockpit,deryni/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,cockpit-project/cockpit,deryni/cockpit