Consider adding OS/system information to test results where relevant

@hardboprobot mentioned in an OOB discussion:

> Currently, the data we keep about a test result includes the kernel version used for it, but for other types of tests where the userspace is a key ingredient (ChromeOS - Yocto - Android), we might want to also encode the ChromeOS userspace version used as part of the test results. Does it makes sense?

Retrieving and storing such information would probably make sense (for ChromeOS it could be the content of `/etc/os-release` -- which is already `cat`'ed in LAVA jobs -- for example).

This needs to be carefully designed as it involves multiple components (e.g. making this information a test result in LAVA) and should be generic enough to be used across various userspaces (Android likely has different way of storing OS-related information).

Start by mapping how LAVA jobs currently expose `/etc/os-release` and how kernel versions are stored in test results. Compare the proposed ChromeOS userspace information with the differing Android approach, then define a generic result format that can work across the mentioned components. Done means the design is agreed for retrieving and storing userspace information without being tied to one operating system.

Written by the indexing model from the issue text.