timeout: Clean up

• Annotate logv() and fix format string bug.

• Don't reinvent str2sig(3).

• Reorganize kill_self() so we unblock signals as late as possible, and use raise(2) instead of kill(2).

• Explicitly close unused pipe descriptors.

• Use correct type to collect result of read(2) and write(2).

• Compare return values to 0, not -1.

• Sort local variables according to style(9).

• Reduce unnecessary nesting.

• Reindent.

• Fix typo in manual page.

MFC after: 1 week
Sponsored by: Klara, Inc.
Reviewed by: kevans
Differential Revision: https://reviews.freebsd.org/D55277

(cherry picked from commit 08208cd694815cc855835960f55231342eb35934)