Add and use find_cartridge_or_raise_exception

Add OpenShift::CartridgeCache::find_cartridge_or_raise_exception, which
wraps find_cartridge and raises OpenShift::OOException if no cartridge
provides the requested feature.

In RestApplication#initialize, RestApplication10#initialize,
RestApplication13#initialize, RestApplication15#initialize,
RestGearGroup#initialize, and RestGearGroup15#initialize, use
find_cartridge_or_raise_exception instead of find_cartridge in place of
repetitive error checking and to perform the error checking in more places.

This commit is related to bug 993440.