Allow one to set configuration when using tomcat package.

When tomcat is installed from packages (in EL), the scripts that
are run to launch tomcat do not source setenv.sh, hence the
tomcat::setenv::entry resource becomes useless for this specific
case.

In order to still be able to control tomcat instances installed
from repository, this PR creates a new resource tomcat::config::entry
that does exactly the same thing as tomcat::setenv::entry but for
default configuration file based on the OS.