Extract inheritFrom and inheritanceType handling from AclBuilder.

This removes inheritFrom and inheritanceType handling from
AclBuilder and moves that responsibility to FsAdaptor, which
has knowledge of ACL inheritance structure.  This refactoring
changes the API to the AclBuilder methods used: eliminating
most passed parameters, and returning a partial populated
Acl.Builder instead of a fully constructed Acl.  This also
requires significant changes to AclBuilderTest.

Code Review: https://codereview.appspot.com/54820046/
3 files changed