git-instaweb: Move all actions at the end of script

git-instaweb: Move all actions at the end of script

As a nice side-effect now the order of parameters does not matter:

  $ git instaweb --httpd=apache2 --start

is now (after this patch) the same as

  $ git instaweb --start --httpd=apache2

Before this commit --start, --stop, --restart (and their subcommand
versions start, stop, restart) exited immediately.

This is preparatory work for making start/restart check that correct
configuration is set up; this change was required to have access in
start_httpd to requested web browser etc.

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Acked-by: Eric Wong <normalperson@yhbt.net>