BACKPORT: tlsdate, docs: make -V taken an optional arg to simplify showtime

Update the man pages and simplify the processing of -V
and --showtime to share the optional argument path.

TEST=manual
BUG=chromium:262137

Change-Id: I42eac2d27c0c2b23ff50b4a3d4b52d376d28e450
Reviewed-on: https://chromium-review.googlesource.com/169980
Reviewed-by: Kees Cook <keescook@chromium.org>
Commit-Queue: Will Drewry <wad@chromium.org>
Tested-by: Will Drewry <wad@chromium.org>
2 files changed