Fix value of `virtual` grain when using `virt-what`
Fix value of `virtual` grain when using `virt-what`

`virt-what` might return multiple lines, depending on what it detected (e.g. `lxc` inside a `HyperV` VM), where the last line corresponds to the most likely match.

Until now, Salt evaluated the whole multi-line output as a single string, which caused quite inaccurate matches. This commit changes this behavior to only evaluate the last line of the `virt-what` output.

A similar issue is described in #25697, but might actually have a different root cause.

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt