removing mod_disk_cache from list of default mods on redhat

While it is indeed loaded on a stock redhat-family apache install, it's not actually enabled, so it shouldn't be listed as a default here.
Remove all mods from default_mods that aren't actually default on redhat
Removing all proxy mods from default_mods on redhat

…since we were forced to remove mod_proxy, and these mods depend on it
fixing tests to match new behavior
Removing mod_authnz_ldap from default_mods since mod_ldap is now removed
Merge pull request #260 from justinclayton/master

default_mods overreaches by implementing much more than stock OS defaults