Use service role with glance service

glance just used to admin role for token validation,
the service role is sufficient for this.

glance also needs an user with enough permission to use swift,
so creating a dedictated service user for swift usage when s-proxy is
enabled.

Change-Id: I6df3905e5db35ea3421468ca1ee6d8de3271f8d1
Merge "Use service role with glance service"