installer: use predefined resource_limits if present

If there is a canned resource_limits.conf.$profile{,.$type} file in
/etc/openshift that matches the profile specified for the node,
openshift.sh will use it from the start by copying it over the default
resource_limits.conf.

Also introduces $CONF_NODE_HOST_TYPE so the above can specify
different resource_limits for different host sizes/flavors.