Describe --results-file in each command

Move the "abstract" description of the --results-file flag supported by
various commands from the kyua-results-files(7) manpage to the manpage
of every command that supports the flag.
Remove the kyua-test-isolation(7) manpage

Fold the contents of kyua-test-isolation(7) into the commands that run
tests so that the information is readily available and more discoverable.
Remove the kyua-results-files(7) manpage

Fold the remaining contents of kyua-results-files(7) into all the places
where they belong.
Fix manbuild to preserve formatting

Make sure manbuild preserves trailing space and backslashes in parsed
files.