base: Don't error on event field values containing '='

[bjackman]

If a trace field value contains a '=', we currently get a ValueError('Too many values to unpack'). Instead, let's only split on the first '='.

In practice if a field value contains a '=' it's probably because a kernel developer typo'd a custom event like:

/* Note missing space between "%d" and "bar" */
trace_printk("my_broken_event: foo=%dbar=%d", foo, bar)

So I did consider raising an explicit 'malformed event field' error. But this approach is more flexible in case someone really wanted to trace fields containing strings with '=' in them.

[JaviMerino]

It should be easy to create a test for this, can you add it as part of this commit?

[bjackman]

Pushed a version with a simple test. I used a .txt trace file because that way it was easy to chop out the relevant bit, is that OK?

[JaviMerino]

It's perfect :heart: , thanks!