Disable unused Apache modules

The alias and autoindex module results in /icons/ serving a list of
Apache icons. We don't need this, and so we disable them.

NOTE for future self: If those modules become necessary, then an option
is to override `templates/default/mods/alias.conf.erb` from the apache2
cookbook.
Release: 6.4.1
Merge pull request #63 from Scalr/release-6.4.1

Release 6.4.1