integration tests use out list instead of results file + patching echo

[yaythomas]

Some of the integration tests are fairly slow & this gets annoying during dev cycles.

Especially the integration tests that read expected output from a _expected file can rewire instead to check a list from the result context, assuming the test pipelines replace pypyr.steps.echo with pypyr.steps.append. This saves at least one file PER TEST being read from disk during test runs.

This can be an incremental task. For starters, will just focus on the slowest offenders - which is tests/integrations/pypyr/call/loopcallnested_int_test.py. These are the only tests that use assert_pipeline_raises_match_file.

Other integration tests that just intercepts echo can also use the pypyr.steps.append technique - these will be updated incrementally over time.