Make apache2 service action configurable.

Assuming the following recipe:
```ruby
include_recipe 'apache2'
include_recipe 'apache2::mod_php5'
template '/etc/apache2/sites-available/mysite.conf' do
# ...
end 
```
If I've made a mistake in the config template, I can't just fix it and rerun Chef since the 'apache2' recipe tries to start the service which of course fails since I haven't reached the line that replaces the faulty config.