git-instaweb: Don't assume Apache executable is named apache2

git-instaweb: Don't assume Apache executable is named apache2

On Arch Linux, the executable for the Apache HTTP server keeps
the 'httpd' name and is not named 'apache2'. The path to the
server modules also contains 'httpd' rather than 'apache2'.
Remove some of these assumptions and add the httpd name in where
it may be required. Finally, make some slight style adjustments
to the code we are touching to make it fit the style of the rest
of the script.

Signed-off-by: Dan McGee <dpmcgee@gmail.com>
Acked-by: Eric Wong <normalperson@yhbt.net>