Report tests results whenever possible

Summary: This adjusts the behavior of PytestTestEngine so that it correctly reports test failures natively, rather than throwing a command error.

Test Plan: Yeah right

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D10866
Update lint engine documentation

Summary: Fixes T6627. This class documentation is out of date and somewhat misleading in the modern environment.

Test Plan: Read it.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T6627

Differential Revision: https://secure.phabricator.com/D10899
Extend `LINT_BRACE_FORMATTING` to warn on missing braces

Summary: Extend the `ArcanistXHPASTLinter::LINT_BRACE_FORMATTING` rule to raise a warning when `n_STATEMENT` is used without having `n_STATEMENT_LIST` as a parent. Essentially, this means that `if ($x) { do_y(); }` is preferred over `if ($x) do_y();`.

Test Plan: Added some test cases.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D10571
Extend `LINT_BRACE_FORMATTING` to support more scenarios

Summary: Extend the `ArcanistXHPASTLinter::LINT_BRACE_FORMATTING` rule to support a bunch of extra cases.

Test Plan: Added test cases.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D10572
Minor linter fixes

Summary: Self explanatory/

Test Plan: `arc lint`

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: aurelijus, Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D10943