Inherit roles for create_trust_context()

This change the default value of the option
'trusts_delegated_roles' to []. And delegate all of
the trustor roles when create the trust unless
user set the option to subset roles.

Change-Id: I3f1b70b78b91bfac9af5fadb71140679b208c999
Closes-bug: #1376562
Merge "Inherit roles for create_trust_context()"