Deprecate show_host_resources() in scheduler manager

This method does not at all belong in the scheduler. Its only use is
from being remotely called by nova-manage to whom it returns data
fetched from the db. I think nova-manage is better of fetching this
data on its own instead of making this extra round trip to the
scheduler.

Change-Id: I435300cdd15bdd041cbe5718ae064b98cec4cceb