ModuleRegistry now cache entry points group

Cache the group entry point instead of each entry individually.

When I originally introduced entry point caching (4deef9ff) I used to
lookup the name and cache it.  Thus, for we ended up doing a new lookup
for each entry point in an entry point group.

Instead, on first lookup, cache the whole group so further entry point
lookup are cache hits.

Change-Id: Ie93ec793bb18a2dadebe736db4c4d33171ceda27
Merge "ModuleRegistry now cache entry points group"