change path to mod passenger.so to support puppet >= 3.9.0.beta on CentOS

path to mod_passenger.so module was changed from ext/apache2/mod_passenger.so
to libout/apache2/mod_passenger.so in version 3.9.0.beta of passenger
(https://github.com/FooBarWidget/passenger/commit/1d7ea010adea0a3f51a)