Allow declaration to override $httpd_dir via parameter

[baconm]

Particularly on RHEL versions, the bundled httpd is many versions behind. For feature or security reasons, many build their own Apache versions and install them in locations with conf dirs other than /etc/httpd.

I propose an httpd_dir parameter passable at class declaration which overrides the OS-default for apache::params::httpd_dir, as follows:

class { 'apache':
httpd_dir = '/usr/local',
}