Change trial's assert method implementation to stop emphasizing the `fail` variations

[exarkun]

Everyone is switching to the assert spellings,  including us.

[exarkun]

(In [35336]) Branching to 'trial-assert-5901'

[exarkun]

(In [35337]) Rename the assertion methods to start with "assert" and make "fail" be the aliases.

refs #5901

[exarkun]

 build results

[Julian]

Looks good to me. Only thing worth pointing out that I see is that assertWarns's def line will fit within 79 chars now.

Also, assertNotIsInstance's docstring is wrong. You're not changing that, so I guess that deserves another ticket if you don't want to fix it while you're here, or if you'd prefer that anyhow. The reason I mention it is that now that the assertion methods are defined using positive language, perhaps all of the docstrings might be clearer if they used that too so that you don't need any mental gymnastics to read them. That can go in another ticket too I guess if that's something reasonable sounding.

[exarkun]

(In [35347]) Fix an incorrect negation in assertNotIsInstance

refs #5901

[exarkun]

(In [35348]) Merge trial-assert-5901

Author: exarkun Reviewer: Julian Fixes: #5901

Change trial's implementation of assertion methods so that they are named following the "assertXYZ" convention rather than the "failXYZ" convention.