Add unique signatures generation to general parse results

[r-c-n]

These changes extend the idea of hash signatures to general parse results, not only errors. This means that all states will now have a unique hash to identify their result based on a set of result fields.

For instance, the generic_boot state collects its key result in the bootloader.done field, so the signature for this result is based on the name and contents of that field.
The kernel_load state has linux.boot.prompt as its key result, so that field will be used to generate the hash key for the state.

Summary fields have also been added to optionally show a human-readable message describing the result.

After logspec goes through a sequence of states, their signature fields will be collected and the hash signature will be generated. The summaries for each state will also be added to a list:

Example: parse a log with the generic_linux_boot parser:

{
    "_match_end": 423922,
    "_signature": "78b6786fda2a517f471e839e93c2c3b17412d089",
    "_signature_fields": [
        "bootloader.done",
        "linux.boot.prompt"
    ],
    "_summary": [
        "Bootloader stage done, jump to kernel",
        "Linux boot prompt found"
    ],
    "bootloader.done": true,
    "errors": [],
    "linux.boot.prompt": true
}

This means that the bootloader finished correctly, handed the execution over to the kernel, the kernel loaded and reached a prompt and no errors were found.

Similar example, this time the kernel didn't reach a prompt:

{
    "_match_end": 374083,
    "_signature": "730f1cab1744a3d79df215388f20b58793a5712c",
    "_signature_fields": [
        "bootloader.done",
        "linux.boot.prompt"
    ],
    "_summary": [
        "Bootloader stage done, jump to kernel",
        "Linux boot prompt not found"
    ],
    "bootloader.done": true,
    "errors": [],
    "linux.boot.prompt": false
}

For logging purposes, if we're interested only in the result of the last state, we can get the last element of the _summary list to get the relevant message.

NOTE that these signatures aren't necessarily related to errors, but to result conditions in general.

[helen-fornazier]

iiuc, _summary is just for states right? Should we rename it to _states_summary ?

I'm also wondering if we couldn't have another flag to say we didn't receive any logs from the kernel at all (not only that prompt wasn't reached)

[r-c-n]

@helen-fornazier thanks for reviewing, answers below:

iiuc, _summary is just for states right? Should we rename it to _states_summary ?

Ah, I thought I had use summary for the errors too, but now that I double check it looks like those are error_summary fields. Yeah, we can change the name, I don't really have a preference.

I'm also wondering if we couldn't have another flag to say we didn't receive any logs from the kernel at all (not only that prompt wasn't reached)

That's something we can try to add yes, let me give it a spin and I'll push some more commits.

[r-c-n]

@helen-fornazier Done, check out this output for the results of your collected logs with these changes.

[helen-fornazier]

@helen-fornazier Done, check out this output for the results of your collected logs with these changes.

nice! Looks good! If we could add a "Kernel didn't started" in the summary it would be even better

[r-c-n]

Done: 6e2bdbb 👍
Updated results here

[helen-fornazier]

looks good to me, I just want to wait for this PR to be merged if you don't mind