Improve tracetools_test and simplify test_tracetools code

[christophebedard]

The main/biggest improvement is the new get_event_with_field_value_and_assert() test method, which can simplify this very common bit of code:

my_events = self.get_events_with_field_value('field', value, events)
self.assertNumEventsEqual(my_events, 1)
my_event = my_events[0]

into:

event = self.get_event_with_field_value_and_assert('field', value, events)

I've therefore updated a lot of test code to use this new assert method, which makes it a lot simpler and smaller.

I also renamed assertValidArray() to assertValidStaticArray() and added length checking.

[fujitatomoya]

lgtm with green CI.

[christophebedard]

• Linux
• Linux-aarch64
• Windows

[christophebedard]

Thanks for the review.