Provide new endpoint routines for admin_endpoint, internal_endpoint,
and public_endpoint. These will allow folks to specify different URLs
for those endpoints if they wish.
This is the first part of the fix. After the routines have been merged,
I'll start working on using the routines in the various component
recipies.
Change-Id: I5b3b90324ee0f9bf6b2c5278ad60724856d43321
Partial-Bug: 1412919